Curable liquids and inks for toys and food packaging applications

ABSTRACT

A free radical curable liquid for inkjet printing of food packaging materials includes no initiator or otherwise one or more initiators selected from the group consisting of non-polymeric di- or multifunctional initiators, oligomeric initiators, polymeric initiators, and polymerizable initiators; and a polymerizable composition of the liquid consists essentially of: a) 25-100 wt % of one or more polymerizable compounds A having at least one acrylate group G1 and at least one second ethylenically unsaturated polymerizable functional group G2 selected from the group consisting of a vinlyether group, an allylether group, and a allylester group; b) 0-55 wt % of one or more polymerizable compounds B selected from the group consisting of monofunctional acrylates and difunctional acrylates; and c) 0-55 wt % of one or more polymerizable compounds C selected from the group consisting of trifunctional acrylates, tetrafunctional acrylates, pentafunctional acrylates and hexafunctional acrylates. If the weight percentage of compounds B&gt;24 wt %, then the weight percentage of compounds C&gt;1 wt %, and all weight percentages of A, B, and C are based upon the total weight of the polymerizable composition. At least one polymerizable compound B or C is present in the polymerizable composition if the free radical curable liquid contains no initiator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2008/064180, filed Oct. 21, 2008. This application claims thebenefit of U.S. Provisional Application No. 60/982,471, filed Oct. 25,2007, which is incorporated by reference herein in its entirety. Inaddition, this application claims the benefit of European ApplicationNo. 07119170.4, filed Oct. 24, 2007, which is also incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to curable inks, more particularly curableinkjet inks and their use in inkjet printing methods for toys and foodpackaging applications.

2. Description of the Related Art

In inkjet printing, tiny drops of ink fluid are projected directly ontoan ink-receiver surface without physical contact between the printingdevice and the ink-receiver. The printing device stores the printingdata electronically and controls a mechanism for ejecting the dropsimage-wise. Printing is accomplished by moving a print head across theink-receiver or vice versa or both.

When jetting the inkjet ink onto an ink-receiver, the ink typicallyincludes a liquid vehicle and one or more solids, such as dyes, pigmentsand polymers. Ink compositions can be roughly divided in:

-   -   water-based, the drying mechanism involving absorption,        penetration and evaporation;    -   solvent-based, the drying primarily involving evaporation;    -   oil-based, the drying involving absorption and penetration;    -   hot melt or phase change, in which the ink is liquid at the        ejection temperature but solid at room temperature and wherein        drying is replaced by solidification; and    -   UV-curable, in which drying is replaced by polymerization.

It should be clear that the first three types of ink compositions aremore suitable for an absorbing ink-receiver, whereas hot melt inks andUV-curable inks can also be printed on non-absorbing ink-receivers. Dueto thermal requirements posed by hot melt inks on the substrates,especially radiation curable inks have gained the interest of theindustry in inkjet printing applications.

Migrateable residues in cured layers of inkjet ink on toys or packagingof foodstuffs may present a health risk and consequently they should bekept to an absolute minimum. In general, UV-curable inks containcolorants, monomers, photoinitiators and polymerization synergists.Known measures to reduce extractables of the photoinitiating system fromcured ink layers include the use of polymeric or co-polymerizablephotoinitiators and synergists instead of the usual low molecular weightcompounds.

For example, US 2006014848 (AGFA) discloses radiation curable inkjetinks including a polymeric co-initiator including a dendritic polymercore with at least one co-initiating functional group as an end group.Aliphatic amines and aromatic amines are included as suitableco-initiating functional groups. The dendritic polymeric architectureallows to obtain low extractables and at the same time to minimize theincrease in viscosity of the ink.

The colorants used in curable inkjet inks can be dyes, but are generallycolour pigments which together with a polymeric dispersant attached tothe surface of the pigment are usually very difficult to extract. Theremaining problem for extractables includes the monomers. The use ofpolymerizable oligomers or crosslinkable polymers instead of lowmolecular weight monomers is only possible up to a certain amount in theink due to limitations of inkjet printing requiring the inks to possessa low viscosity at the jetting temperature.

In general, the curable inkjet inks are cured by radiation. Thermalcuring and electron beam curing of inkjet inks are alternatives for themore preferred radiation curing, more particularly UV-radiation curing.The polymerization mechanism is usually either free radicalpolymerization or cationic polymerization. There is widespread beliefthat cationic inkjet inks would be more suitable for food packagingapplications. Cationic inkjet inks tend to polymerize slower than freeradical polymerizable inkjet inks but to a larger extent. This meansthat free radical inkjet inks polymerize much faster but the cured imagelayer contains more extractables, i.e. unreacted monomers.

U.S. Pat. No. 6,803,112 (SUN CHEMICAL) discloses a method for producinga low-extractable film packaging from an actinic radiation curableaqueous composition containing a water soluble compound having at leastone α,β-ethylenically unsaturated, radiation polymerizable group andwater as essential components carried out by applying the aqueouscomposition to a surface which is then irradiated in a single step withactinic radiation in the presence of the water thereby forming a curedfilm wherein less than 50 ppb of the water soluble compound or itsresidual components are extractable by a food simulant.

The volatility of some of these monomers in curable inkjet inks alsocontribute to unpleasant odors from printed matter. For non-foodprinting applications, these unpleasant odors have been camouflaged byaddition of deodorizers. For example, US 2005287476 (KONICA MINOLTA)discloses photocurable compositions including a photopolymerizablecompound, a photoinitiator and a compound selected from the groupconsisting of a deodorizer, a perfume and an antioxidant. Also EP1721943 A (FUJI) discloses the use of flagrances in a curable ink.

US 2003199655 (NIPPON CATALYTIC CHEM) discloses an activated energyray-curable ink composition for ink-jet printing including a diluentaccording to Table 1 containing substantially VEEA and monofunctionalphotoinitiator.

WO 2006/085992 A (HEXION) discloses a radiation curable inkjet inkincluding a radiation curable composition including about 0.1 to about15 wt. % of an ethylenically unsaturated mono functional monomer, about30 to about 80 wt. % of an ethylenically unsaturated difunctionalmonomer and may further include VEEA and monofunctional photoinitiator.

U.S. Pat. No. 6,310,115 B1 (AGFA) discloses ultraviolet curable inkcompositions for ink jet printing including an ultraviolet curablemonomer having a vinylether function and a (meth)acrylate function.

Therefore, it would be desirable to have curable inkjet inks thatcombine the best of both worlds, i.e. the high curing speed of freeradical inkjet inks and the complete curing of cationic curable inkjetinks. Furthermore, a need continues to exist for radiation-curableinkjet inks that do not cause bad smell without adding deodorizers orperfumes.

SUMMARY OF THE INVENTION

A preferred embodiment of the invention provides inkjet inks exhibitingimproved complete curing and high curing speed, making them moresuitable for food packaging applications.

Another preferred embodiment of the invention provides inkjet inksexhibiting a good stability.

Another preferred embodiment of the invention provides printed matterexhibiting no or almost no unpleasant odors without using deodorizers tomask the unpleasant odor.

These and other preferred embodiments of the invention will becomeapparent from the description hereinafter.

It was found that inkjet inks exhibited improved complete curing andhigh curing speed, as well as improved adhesion and reduced unpleasantodors by using a specific composition including a sufficient amount ofspecific monomers. Very low amounts of extractables were found afterfull curing, which opened perspective for radiation curable inkjetapplications for food and toys.

Preferred embodiments of the invention have been realised with a freeradical curable liquid as defined below.

Preferred embodiments of the invention have also been realised with aninkjet printing method as defined below.

Further advantages and embodiments of the present invention will becomeapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE shows desorption chromatograms of volatile extractables fromcured samples of free radical curable liquids coated on a substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Definitions

The term “dye”, as used in disclosing the present invention, means acolorant having a solubility of 10 mg/L or more in the medium in whichit is applied and under the ambient conditions pertaining.

The term “pigment” is defined in DIN 55943, herein incorporated byreference, as a colorant that is practically insoluble in theapplication medium under the pertaining ambient conditions, hence havinga solubility of less than 10 mg/L therein.

The term “monofuntional initiator”, as used in disclosing the presentinvention, means an initiator having only one initiating functionalgroup.

The term “difuntional initiator”, as used in disclosing the presentinvention, means an initiator having two initiating functional groups.

The term “multifuntional initiator”, as used in disclosing the presentinvention, means an initiator having more than two initiating functionalgroups.

The term “C.I.” is used in disclosing the present application as anabbreviation for Colour Index.

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. for three carbon atoms: n-propyl andisopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl;for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyland 2-methyl-butyl etc.

The terms “weight %”, “wt %” and “weight percentage” all have the samemeaning.

The term “actinic radiation” as used in disclosing the presentinvention, means electromagnetic radiation capable of initiatingphotochemical reactions.

The term “ultraviolet radiation” as used in disclosing the presentinvention, means electromagnetic radiation in the wavelength range ofabout 100 to about 400 nanometers.

Curable Liquids and Inks

The free radical curable liquid or ink according to a preferredembodiment of the present invention includes no initiator or otherwiseone or more initiators selected from the group consisting ofnon-polymeric di- or multifunctional initiators, oligomeric initiators,polymeric initiators and polymerizable initiators; wherein thepolymerizable composition of the liquid consists essentially of: a)25-100 wt % of one or more polymerizable compounds A having at least oneacrylate group G1 and at least one second ethylenically unsaturatedpolymerizable functional group G2 selected from the group consisting ofa vinlyether group, an allylether group and a allylester group; b) 0-55wt % of one or more polymerizable compounds B selected from the groupconsisting of monofunctional acrylates and difunctional acrylates; andc) 0-55 wt % of one or more polymerizable compounds C selected from thegroup consisting of trifunctional acrylates, tetrafunctional acrylates,pentafunctional acrylates and hexafunctional acrylates, with the provisothat if the weight percentage of compounds B>24 wt %, then the weightpercentage of compounds C>1 wt %; and wherein all weight percentages ofA, B and C are based upon the total weight of the polymerizablecomposition; and with the proviso that at least one polymerizablecompound B or C is present in the polymerizable composition if the freeradical curable liquid contains no initiator.

The curable liquid according to a preferred embodiment of the presentinvention is preferably a curable inkjet liquid, more preferably aradiation curable inkjet liquid, and most preferably a UV radiationcurable inkjet liquid.

The curable liquid preferably includes at least one photoinitiator.

The curable liquid is preferably part of an inkjet ink set wherein atleast one, more preferably all inks have a curable composition accordingto the present invention.

The curable liquid may contain one or more colour pigments as colorant,and at that moment a skilled person refers to it as a curable inkinstead of a curable liquid.

A curable inkjet ink set preferably includes at least one yellow curableinkjet ink (Y), at least one cyan curable inkjet ink (C) and at leastone magenta curable inkjet ink (M) and preferably also at least oneblack curable inkjet ink (K). The curable CMYK inkjet ink set may alsobe extended with extra inks such as red, green, blue, and/or orange tofurther enlarge the colour gamut of the image. The CMYK ink set may alsobe extended by the combination of full density and light density inks ofboth colour inks and/or black inks to improve the image quality bylowered graininess.

In a preferred embodiment, the radiation curable inkjet ink set is aUV-curable pigment inkjet ink set.

The curable liquid or ink may further also contain at least oneinhibitor.

The curable liquid or ink may further also contain at least onesurfactant.

The curable liquid or ink is most preferably a non-aqueous inkjet liquidor ink. The term “non-aqueous” refers to a liquid carrier which shouldcontain no water. However sometimes a small amount, generally less than5 wt % of water based on the total weight of the ink, can be present.This water was not intentionally added but came into the formulation viaother components as a contamination, such as for example polar organicsolvents. Higher amounts of water than 5 wt % tend to make thenon-aqueous inkjet inks instable, preferably the water content is lessthan 1 wt % based on the total weight dispersion medium and mostpreferably no water at all is present.

The curable liquid or ink preferably does not contain an evaporablecomponent such as an organic solvent. But sometimes it can beadvantageous to incorporate a small amount of an organic solvent toimprove adhesion to the surface of a substrate after UV-curing. In thiscase, the added solvent can be any amount in the range that does notcause problems of solvent resistance and VOC, and preferably 0.1-10.0 wt%, and particularly preferably 0.1-5.0 wt %, each based on the totalweight of the curable ink.

The pigmented curable ink preferably contains a dispersant, morepreferably a polymeric dispersant, for dispersing the pigment. Thepigmented curable ink may contain a dispersion synergist to improve thedispersion quality of the ink. Preferably, at least the magenta inkcontains a dispersion synergist. A mixture of dispersion synergists maybe used to further improve dispersion stability.

The viscosity of the ink is preferably smaller than 100 mPa·s at 30° C.and at a shear rate of 100 s⁻¹. The viscosity of the inkjet ink ispreferably smaller than 30 mPa·s, more preferably lower than 15 mPa·s,and most preferably between 2 and 10 mPa·s at a shear rate of 100 s⁻¹and a jetting temperature between 10 and 70° C.

The polymerizable compounds used in the curable ink, especially for foodpackaging applications, are preferably purified compounds having no oralmost no impurities, more particularly no toxic or carcinogenicimpurities. The impurities are usually derivative compounds obtainedduring synthesis of the polymerizable compound. Sometimes, however, somecompounds may be added deliberately to pure polymerizable compounds inharmless amounts, for example, polymerization inhibitors or stabilizers.

Polymerizable Compounds A

The free radical curable liquid for inkjet printing of food packagingmaterials includes one or more polymerizable compounds A having at leastone acrylate group G1 and at least one second ethylenically unsaturatedpolymerizable functional group G2 selected from the group consisting ofa vinlyether group, an allylether group and a allylester group.

In a preferred embodiment, the one or more initiators are polymerizableinitiators, e.g. possessing one or two acrylate groups. In the lattercase the photopolymerizable initiator must be regarded as apolymerizable compound B of the free radical curable liquid according toa preferred embodiment of present invention. Consequently the weightpercentage of the one or more polymerizable compounds A must be smallerthan 100. This is also true for other types of compounds, for example,polymerizable surfactants, polymerizable inhibitors and polymerizableco-initiators. In these cases the content of compound A of the curableliquid or ink according to preferred embodiments of the presentinvention is preferably smaller than 99 wt %, more preferably smallerthan 98 wt % and most preferably smaller than 95 wt % all based upon thetotal weight of the polymerizable composition.

The curable liquid or ink according to a preferred embodiment of thepresent invention includes a polymerizable composition consistingessentially of one or more polymerizable compounds A and optionally oneor more polymerizable compounds B and/or polymerizable compounds C. Thewording “consisting essentially” in the present invention means thatother polymerizable compounds different from the compounds A, B and Cmay be used as long as they do not lead to large amounts of extractablesfrom the cured layer. For example, a polymerizable compound having twovinylether groups but no acrylate group can be added to thepolymerizable composition of the curable liquid or ink only in smallamounts without causing large amounts of extractables. Amounts of 25 wt% or more of a divinylether compound based upon the total weight of thepolymerizable composition do not result in curable liquids or inkssuitable for inkjet printing on toys or food packaging applications. Theamount of polymerizable compounds different from the polymerizablecompounds A, B and C should preferably be smaller than 5 wt % and morepreferably smaller than 2 wt % based upon the total weight of thepolymerizable composition. Most preferably no other polymerizablecompounds other than the polymerizable compounds A, B and C are presentin the curable liquid or ink, i.e. the polymerizable liquid or inkconsists of one or more polymerizable compounds A and optionally one ormore polymerizable compounds B and/or polymerizable compounds C. Itshould also be noted that at least one acrylate group is present in thepolymerizable compounds A, B and C. Replacement of the acrylate group bya methacrylate group does not result in curable liquids or inks suitablefor inkjet printing on toys or food packaging applications.

The free radical curable liquid and inks according to a preferredembodiment of the present invention preferably include a polymerizablecomposition including 60 to 90 wt % of one or more polymerizablecompounds A and 10 to 40 wt % of one or more polymerizable compounds C,both based upon the total weight of the polymerizable composition.

The rate and the completeness of a polymerization can be influencedthrough the type and concentration of monofunctional and polyfunctionalmonomers in the ink. Monofunctional monomers have only one polymerizablefunctional group for taking part in the polymerization process andusually also exhibit a lower viscosity, whereby the polymerization cancontinue for a longer time than polyfunctional monomers, but at the endresults in a certain amount of unreacted monomers trapped in thepolymerized layer. Generally, polyfunctional monomers have largerprobability of taking part in the polymerization because they have twoor more polymerizable functional groups. However, because they can reactmore rapidly and frequently, vitrification of the layer occurs muchfaster leading to unreacted polyfunctional monomers getting trapped inthe polymerized network. These trapped monomers contribute significantlyto the extractables which limit the possibilities for inkjet printing intoys and food packaging applications.

The polymerizable compound A is preferably represented by the Formula(I):

whereinG1 represents an acrylate group;G2 represents an ethylenically unsaturated polymerizable functionalgroup selected from the group consisting of a vinylether group, anallylether group and a allylester group; GX and GY are independentlyselected from the group consisting of G1 and G2;n and m are independently selected integers having a value of 0 or 1;andL represents a (n+m+2)-valent linking group including at least onecarbon atom. For example is n=1 and m=0 than the (n+m+2)-valent linkinggroup represents a trivalent linking group including at least one carbonatom. In a preferred embodiment, the integers n and m both have a valueequal to 0.

In a preferred embodiment the linking group is an aliphatic chain,preferably including 1 to 6 carbon atoms.

In another preferred embodiment the linking group includes one or moreethyleneoxide units and/or one or more propyleneoxide units.

A single polymerizable compound A may be used in the ink or a mixture ofdifferent polymerizable compounds A may be used as long as the totalamount of the different polymerizable compounds A expressed as weight %stays within the defined range for the one or more polymerizablecompounds A.

In a preferred embodiment, the polymerizable compound A has one or morevinylether groups as second polymerizable functional group G2.

In another preferred embodiment, the polymerizable compound A has one ormore allylether groups as second polymerizable functional group G2.

In another preferred embodiment, the polymerizable compound A has one ormore allylester groups as second polymerizable functional group G2.

In a very preferred embodiment, the polymerizable compound A is2-(vinylethoxy)ethyl acrylate.

Typical polymerizable compounds suitable for the curable liquids andinks according to preferred embodiments of the present invention areshown in Table 1, without being limited thereto.

TABLE 1 PC -1

PC-2

PC-3

PC-4

PC-5

PC-6

PC-7

PC-8

PC-9

PC-10

The polymerizable compound A preferably has a molecular weight smallerthan 800 Dalton, more preferably smaller than 500 Dalton, and mostpreferably smaller than 400 Dalton.

The polymerizable compound A can be advantageously used for reducing theextractables from an image layer.

The polymerizable compound A can also be advantageously used forreducing unpleasant odors from printed matter.

Other Polymerizable Compounds

The polymerizable compound A may be combined in the ink with anothermonomer or oligomers having at least one acrylate group.

A combination of other monomers and/or oligomers may also be used. Themonomers and/or oligomers may possess different degrees offunctionality, and a mixture including combinations of mono-, di-, tri-and higher functionality monomers and/or oligomers may be used. Theviscosity of the curable ink may be adjusted by varying the ratiobetween the monomers and/or oligomers.

Any polymerizable compound commonly known in the art may be employed andincludes monofunctional and/or polyfunctional acrylate monomers andoligomers.

Suitable monofunctional acrylates include caprolactone acrylate, cyclictrimethylolpropane formal acrylate, ethoxylated nonyl phenol acrylate,isodecyl acrylate, isooctyl acrylate, octyldecyl acrylate, alkoxylatedphenol acrylate, tridecyl acrylate, isoamyl acrylate, stearyl acrylate,lauryl acrylate, octyl acrylate, decyl acrylate, isoamylstyl acrylate,isostearyl acrylate, 2-ethylhexyl-diglycol acrylate, 2-hydroxybutylacrylate, 2-acryloyloxyethylhexahydrophthalic acid, butoxyethylacrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycolacrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycolacrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornylacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethylsuccinic acid,2-acryloyxyethylphthalic acid, 2-acryloxyethyl-2-hydroxyethyl-phthalicacid, lactone modified flexible acrylate and t-butylcyclohexyl acrylate.

Suitable difunctional acrylates include alkoxylated cyclohexanonedimethanol diacrylate, alkoxylated hexanediol diacrylate, dioxane glycoldiacrylate, dioxane glycol diacrylate, cyclohexanone dimethanoldiacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate,triethylene glycol diacrylate, tetraethylene glycol diacrylate,polyethylene glycol diacrylate, dipropylene glycol diacrylate,tripropylene glycol diacrylate, polypropylene glycol diacrylate,1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanedioldiacrylate, neopentyl glycol diacrylate, dimethylol-tricyclodecanediacrylate, bisphenol A EO (ethylene oxide) adduct diacrylate, bisphenolA PO (propylene oxide) adduct diacrylate, hydroxypivalate neopentylglycol diacrylate, propoxylated neopentyl glycol diacrylate, alkoxylateddimethyloltricyclodecane diacrylate and polytetramethylene glycoldiacrylate.

Suitable trifunctional acrylates include propoxylated glycerinetriacrylate, propoxylated trimethylolpropane triacrylate,trimethylolpropane triacrylate, EO modified trimethylolpropanetriacrylate, tri (propylene glycol) triacrylate, caprolactone modifiedtrimethylolpropane triacrylate and pentaerythritol triacrylate,

Suitable higher functional acrylates include pentaerithritoltetraacrylate, pentaerythritolethoxy tetraacrylate, dipentaerythritolhexaacrylate, ditrimethylolpropane tetraacrylate, glycerinpropoxytriacrylate, caprolactam modified dipentaerythritol hexaacrylate,di-trimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate,ethoxylated pentaerythritol tetraacrylate, methoxylated glycol acrylatesand acrylate esters.

Polymerizable oligomers which may be used, include epoxy acrylates,aliphatic urethane acrylates, aromatic urethane acrylates, polyesteracrylates, and straight-chained acrylic oligomers.

Initiators

The curable ink according to a preferred embodiment of the presentinvention preferably contains a photoinitiator or photoinitiator systemsuch as, for example, one or more photoinitiators and one or moreco-initiators. The photoinitiator or photoinitiator system absorbs lightand is responsible for the production of initiating species, i.e. freeradicals which induce the polymerization of monomers, oligomers andpolymers and with polyfunctional monomers and oligomers thereby alsoinduce cross-linking.

Irradiation with actinic radiation may be realized in two steps bychanging wavelength or intensity. In such cases it is preferred to use 2types of photoinitiator together.

Free radical photoinitiators can act as a Norrish type I or a Norrishtype II initiator. Tertiary amines are today admixed to free radicalpolymerizable radiation curable formulations for two main reasons:

i) They counteract air inhibition, provided that the particular aminecontains abstractable α-hydrogens, by formation of radicals, which canparticipate and trigger radical polymerisation of acrylic groups.Tertiary amines can therefore be used together with Norrish type Iphotoinitiators to reduce air inhibition and thereby increase curespeed; andii) They can act as co-initiators together with ketones, for example, ofthe benzophenone type, wherein the excited keto groups abstract ahydrogen from the amine, whereby radicals are formed promoting radicalpolymerisation of acrylic groups and the like. This is the so calledNorrish type II of photopolymerization.

For safety reasons, in particular for food packaging applications, thecurable liquid according to a preferred embodiment of the presentinvention contains a so-called diffusion hindered photoinitiator. Adiffusion hindered photoinitiator is a photoinitiator which exhibits amuch lower mobility in a cured layer of the curable liquid or ink than amonofunctional photoinitiator, such as benzophenone. Several methods canbe used to lower the mobility of the photoinitiator. One way is toincrease the molecular weight of the photoinitiator so that thediffusion speed is reduced, e.g. difunctional photoinitiators orpolymeric photoinitiators. Another way is to increase its reactivity sothat it is built into the polymerizing network, e.g. multifunctionalphotoinitiators and polymerizable photoinitiators. The diffusionhindered photoinitiator is preferably selected from the group consistingof non-polymeric di- or multifunctional photoinitiators, oligomeric orpolymeric photoinitiators and polymerizable photoinitiators.Non-polymeric di- or multifunctional photoinitiators are considered tohave a molecular weight between 300 and 900 Dalton. Monofunctionalphotoinitiators with a molecular weight in that range are not diffusionhindered photoinitiators. Both type I and type II photoinitiators can beused in the present invention, alone or in combination. Most preferablythe diffusion hindered photoinitiator is a polymerizable initiator.

A preferred amount of diffusion hindered photoinitiator is 0-50 wt %,more preferably 0.1-20 wt %, and most preferably 0.3-15 wt % of thetotal weight of the curable ink.

A suitable diffusion hindered photoinitiator may contain one or morephotoinitiating functional groups derived from a Norrish typeI-photoinitiator selected from the group consisting of benzoinethers,benzil ketals, α,α-dialkoxyacetophenones, α-hydroxyalkylphenones,α-aminoalkylphenones, acylphosphine oxides, acylphosphine sulphides,α-haloketones, α-halosulfones and phenylglyoxalates.

A suitable diffusion hindered photoinitiator may contain one or morephotoinitiating functional groups derived from a Norrish typeII-initiator selected from the group consisting of benzophenones,thioxanthones, 1,2-diketones and anthraquinones.

Other photoinitiators suitable for the photoinitiating functional groupsin preparing diffusion hindered photoinitiators are disclosed byCRIVELLO, J. V., et al.; Chemistry & technology of UV & EB Formulationfor Coatings, Inks & Paints. Volume III: Photoinitiators for FreeRadical, Cationic & Anionic Photopolymerisation, 2nd edition, John Wiley& Sons Ltd in association with SITA Technology Ltd, London, UK, 1998edited by Dr. G. Bradley; ISBN 0471 978922, page 287-294.

Difunctional and Multifunctional Photoinitiators

Typical non-polymeric di- and multifunctional initiators have beendisclosed in WO 2005/040083 (LAMBERTI S.P.A), WO 2004/099262 (CIBASPECIALTY CHEMICALS) and Burrows et al., Surface Coatings International,Part B: Coatings Transactions 87(B2), 127-135 (2004) and by Ye et al.,Polymer 47(13), 4603-4612 (2006).

Suitable non-polymeric multifunctional initiators are given below inTable 2 without being limited thereto.

TABLE 2 INI-A1

INI-A2

INI-A3

INI-A4

INI-A5

INI-A6

INI-A7

INI-A8

INI-A9

INI-A10

In comparison with their monofunctional analogues, it was observed thatnon-polymeric di- and multifunctional photoinitiators resulted in farless detectable extractables. Another advantage, especially for inkjetinks, is that non-polymeric di- and multifunctional photoinitiators havelimited or no influence on the viscosity, contrary to the polymericphotoinitiators.

Polymeric Photoinitiators

Suitable polymeric initiators have been recently reviewed by Hrdlovic P.(Polymer News, 30(6), 179-182 (2005) and Polymer News, 30(8), 248-250(2005)) and Corrales T. (Journal of Photochemistry and Photobiology A:Chemistry 159 (2003), 103-114). Further interesting polymericphotoinitiators can be found in CRIVELLO, J. V., et al.; Chemistry &technology of UV & EB Formulation for Coatings, Inks & Paints. VolumeIII: Photoinitiators for Free Radical, Cationic & AnionicPhotopolymerisation, 2nd edition, John Wiley & Sons Ltd in associationwith SITA Technology Ltd, London, UK, 1998 edited by Dr. G. Bradley;ISBN 0471 978922, page 208-224.

Particularly suitable polymeric and oligomeric photoinitiators have beendisclosed by Bertens et al. (RadTech Europe 05, Conference Proceedings(2005) 1, 473-478), by WO 03/033452 (COATES BROTHERS) and by WO03/033492 (COATES BROTHERS).

For reasons of obtaining low viscosity, the preferred polymericarchitecture used in jettable radiation curable compositions and inkjetinks is a dendritic polymeric architecture, more preferably ahyperbranched polymeric architecture. Preferred hyperbranched polymericphotoinitiators are those disclosed in US 2006014851 (AGFA) and US2006014853 (AGFA) incorporated herein as a specific reference.

Suitable polymeric and oligomeric initiators are given below in Table 3without being limited thereto. The hyperbranched structures (INI-B1,INI-B4 and INI-B11) are illustrated with one specific molecular weightand degree of substitution out of the mixture for the sake of clarity.

TABLE 3 INI- B1

INI- B2

n = 5 on average INI- B3

n = 15 on average INI- B4

INI- B5

derived from pentaerythritol ethoxylate (15/4 EO/OH) INI- B6

derived from pentaerythritol ethoxylate (15/4 EO/OH) INI- B7

derived from poly(ethylene glycol) bis(carboxymethyl) ether with MW of250 INI- B8

derived from poly(ethylene glycol) bis(carboxymethyl) ether with MW of600 INI- B9

derived from poly(ethylene glycol) with MW of 200 INI- B10

derived from poly(ethylene glycol) with MW of 600 INI- B11

Polymerizable Photoinitiators

Suitable polymerizable photoinitiators have been disclosed in DE 3534645(MERCK) and EP 0377191 A (BASF). Other suitable polymerizablephotoinitiators have been disclosed by Baeumer et al. (RADCUR '86,Conference Proceedings (1986), 4/43-4/55), Ruhlmann et al. (EuropeanPolymer Journal, 28(9), 1063-1067 (1992)) and Allen et al. (Journal ofPhotochemistry and Photobiology, A: Chemistry: 130(1,2), 185-189(1997)).

In a preferred embodiment the polymerizable photoinitiator includes atleast one (meth)acrylate group, most preferably at least one acrylategroup.

Preferred polymerizable photoinitiators are given below in Table 4,without being limited thereto.

TABLE 4 INI-C1

INI-C2

INI-C3

INI-C4

INI-C5

INI-C6

INI-C7

INI-C8

INI-C9

INI-C10

INI-C11

INI-C12

INI-C13

Diffusion Hindered Co-Initiators

When one or more co-initiators are included into the curable liquid orink according to a preferred embodiment of the present invention,preferably these co-initiators are diffusion hindered.

A diffusion hindered co-initiator is preferably selected from the groupconsisting of non-polymeric di- or multifunctional co-initiators,oligomeric or polymeric co-initiators and polymerizable co-initiators.More preferably the diffusion hindered co-initiator is selected from thegroup consisting of polymeric co-initiators and polymerizableco-initiators. Most preferably the diffusion hindered co-initiator is apolymerizable co-initiator.

A preferred diffusion hindered co-initiator is a polymeric co-initiatorhaving a dendritic polymeric architecture, more preferably ahyperbranched polymeric architecture. Preferred hyperbranched polymericco-initiators are those disclosed in US 2006014848 (AGFA) incorporatedherein as a specific reference.

A more preferred diffusion hindered co-initiator is one or morepolymerizable co-initiators. In a preferred embodiment the polymerizableco-initiator includes at least one (meth)acrylate group, most preferablyat least one acrylate group.

A preferred polymerizable co-initiator is a co-initiator according toFormula (CO-I):

wherein,R¹ and R² are independently selected from the group consisting of analkyl group, an alkenyl group, an alkynyl group, an aralkyl group, analkaryl group, an aryl group and a heteroaryl group;R³ to R⁶ are independently selected from the group consisting ofhydrogen, an alkyl group, an alkenyl group, an alkynyl group, an acylgroup, a thioalkyl group, an alkoxy group, a halogen, an aralkyl group,an alkaryl group, an aryl group and a heteroaryl group;R⁷ is selected from the group consisting of hydrogen, an aldehyde group,a ketone group, an ester group, an amide group, an acyl group, athioalkyl group, an alkoxy group, a halogen, a nitrile group, asulphonate group, a sulphonamide group, an alkyl group, an alkenylgroup, an alkynyl group, an aralkyl group, an alkaryl group, an arylgroup and a heteroaryl group;R¹ and R², R¹ and R³, R² and R⁵, R³ and R⁴, R⁴ and R⁷, R⁸ and R⁶, and R⁶and R⁷ may represent the necessary atoms to form a 5- to 8-memberedring; and with the proviso that the aromatic amine has at least one Alfahydrogen; andat least one of R¹ to R⁷ includes a polymerizable ethylenicallyunsaturated functional group selected from the group consisting ofacrylate, substituted acrylate, methacrylate, styrene, acrylamide,methacrylamide, allyl ester, allyl ether, vinyl ester, vinyl ether,fumarate, maleate, maleimide and vinyl nitrile. In the polymerizableco-initiator, preferably R⁷ represents an electron withdrawing groupselected from the group consisting of an aldehyde, a ketone, an esterand an amide, and more preferably R³, R⁴, R⁵ and R⁶ all representhydrogen.

The alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups,alkaryl groups, aryl groups and heteroaryl groups used for R¹ to R⁷ canbe substituted or unsubstituted groups, i.e. a substituted orunsubstituted alkyl group, a substituted or unsubstituted alkenyl group,a substituted or unsubstituted alkynyl group, a substituted orunsubstituted aralkyl group, a substituted or unsubstituted alkarylgroup and a substituted or unsubstituted (hetero)aryl group may be used.

In a preferred embodiment, the polymerizable co-initiator corresponds toFormula (CO-II):

wherein,R¹ to R⁶ have the same meaning as defined for Formula (CO-I);X is selected from the group consisting of O, S and NR⁹;R⁸ and R⁹ are independently selected from the group consisting ofhydrogen, an alkyl group, an alkenyl group, an alkynyl group, an aralkylgroup, an alkaryl group, an aryl group and a heteroaryl group;R¹ and R², R¹ and R², R² and R⁵, R³ and R⁴, R⁵ and R⁶, R⁴ and R⁶, R⁶ andR⁸, and R⁸ and R⁹ may represent the necessary atoms to form a 5- to8-membered ring; and at least one of R¹ to R⁶ and R⁸ includes apolymerizable ethylenically unsaturated functional group selected fromthe group consisting of acrylate, substituted acrylate, methacrylate,styrene, acrylamide, methacrylamide, allyl ester, allyl ether, vinylester, vinyl ether, fumarate, maleate, maleimide and vinyl nitrile. Inthe polymerizable co-initiator, preferably R³, R⁴, R⁵ and R⁶ allrepresent hydrogen.

In one preferred embodiment of the polymerizable co-initiator havingFormula (CO-II), R¹ represents methyl or ethyl and R² includes apolymerizable ethylenically unsaturated functional group selected fromthe group consisting of acrylate, substituted acrylate, methacrylate,styrene, acrylamide, methacrylamide, allyl ester, allyl ether, vinylester, vinyl ether, fumarate, maleate, maleimide and vinyl nitrile; andmore preferably also R³, R⁴, R⁵ and R⁶ all represent hydrogen.

In another preferred embodiment of the polymerizable co-initiator havingFormula (CO-II), R1 and R² independently represent methyl or ethyl andR⁸ includes a polymerizable ethylenically unsaturated functional groupselected from the group consisting of acrylate, substituted acrylate,methacrylate, styrene, acrylamide, methacrylamide, allyl ester, allylether, vinyl ester, vinyl ether, fumarate, maleate, maleimide and vinylnitrile; and more preferably also R³, R⁴, R⁵ and R⁶ all representhydrogen.

In a more preferred embodiment, the polymerizable co-initiatorcorresponds to Formula (CO-III):

R¹ and R² are independently selected from the group consisting ofmethyl, ethyl, propyl and butyl;L represents a divalent linking group including at least one carbonatom; andR¹⁰ represents hydrogen, methyl, ethyl, propyl or butyl.

In a preferred embodiment the divalent linking group L includes 1 to 30carbon atoms, more preferably 2 to 10 carbon atoms and most preferably 3to 6 atoms.

The polymerizable co-initiator may contain two, three or morepolymerizable ethylenically unsaturated functional groups independentlyselected from the group consisting of acrylate, substituted acrylate,methacrylate, styrene, acrylamide, methacrylamide, allyl ester, allylether, vinyl ester, vinyl ether, fumarate, maleate, maleimide and vinylnitrile.

The polymerizable co-initiator may also contain more than one tertiaryamine functional group, preferably the second or third tertiary aminefunctional group is also an aromatic tertiary amine, most preferably adialkylamino benzoic acid derivative.

Suitable polymerizable co-initiators are given below in Table 5 withoutbeing limited thereto.

TABLE 5 COINI-1

COINI-2

COINI-3

COINI-4

COINI-5

COINI-6

COINI-7

COINI-8

COINI-9

COINI-10

COINI-11

COINI-12

COINI-13

COINI-14

COINI-15

COINI-16

COINI-17

COINI-18

COINI-19

COINI-20

COINI-21

The curable ink preferably includes the polymerizable co-initiator in anamount of 0.1 to 50 wt %, more preferably in an amount of 0.5 to 25 wt%, most preferably in an amount of 1 to 10 wt % of the total weight ofthe ink.

Colorants

The curable ink may contain a colorant. Colorants used in the curableinks may be dyes, pigments or a combination thereof. Organic and/orinorganic pigments may be used.

The colorant is preferably a pigment or a polymeric dye, most preferablya pigment. In food packaging applications, low molecular weight dyes,e.g. smaller than 1000 Dalton, can still migrate into the food or beextracted by the food giving undesired coloration of the food, or evenworse allergic reactions after consuming the solid or liquid food. Mostpreferably the colorant is a pigment.

The pigments may be black, white, cyan, magenta, yellow, red, orange,violet, blue, green, brown, mixtures thereof, and the like. This colourpigment may be chosen from those disclosed by HERBST, Willy, et al.Industrial Organic Pigments, Production, Properties, Applications. 3rdedition. Wiley—VCH, 2004. ISBN 3527305769.

Particular preferred pigments are C.I. Pigment Yellow 1, 3, 10, 12, 13,14, 17, 55, 65, 73, 74, 75, 83, 93, 97, 109, 111, 120, 128, 138, 139,150, 151, 154, 155, 175, 180, 181, 185, 194 and 213.

Particular preferred pigments are C.I. Pigment Red 17, 22, 23, 41, 48:1,48:2, 49:1, 49:2, 52:1, 57:1, 81:1, 81:3, 88, 112, 122, 144, 146, 149,169, 170, 175, 176, 184, 185, 188, 202, 206, 207, 210, 216, 221, 248,251, 254, 255, 264, 266, 270 and 272.

Particular preferred pigments are C.I. Pigment Violet 1, 2, 19, 23, 32,37 and 39.

Particular preferred pigments are C.I. Pigment Blue 15:1, 15:2, 15:3,15:4, 15:6, 16, 56, 61 and (bridged) aluminium phthalocyanine pigments.

Particular preferred pigments are C.I. Pigment Orange 5, 13, 16, 34, 40,43, 59, 66, 67, 69, 71 and 73.

Particular preferred pigments are C.I. Pigment Green 7 and 36.

Particular preferred pigments are C.I. Pigment Brown 6 and 7.

Suitable pigments include mixed crystals of the above particularpreferred pigments. Mixed crystals are also referred to as solidsolutions. For example, under certain conditions different quinacridonesmix with each other to form solid solutions, which are quite differentfrom both physical mixtures of the compounds and from the compoundsthemselves. In a solid solution, the molecules of the components enterinto the same crystal lattice, usually, but not always, that of one ofthe components. The x-ray diffraction pattern of the resultingcrystalline solid is characteristic of that solid and can be clearlydifferentiated from the pattern of a physical mixture of the samecomponents in the same proportion. In such physical mixtures, the x-raypattern of each of the components can be distinguished, and thedisappearance of many of these lines is one of the criteria of theformation of solid solutions. A commercially available example isCinquasia Magenta RT-355-D from Ciba Specialty Chemicals.

Carbon black is preferred as a black pigment. Suitable black pigmentsinclude carbon blacks such as Pigment Black 7 (e.g. Carbon Black MA8®from MITSUBISHI CHEMICAL), REGAL® 400R, MOGUL® L, ELFTEX® 320 from CABOTCo., or Carbon Black FW18, Special Black 250, Special Black 350, SpecialBlack 550, PRINTEX® 25, PRINTEX® 35, PRINTEX® 55, PRINTEX® 90, PRINTEX®150T from DEGUSSA. Additional examples of suitable pigments aredisclosed in U.S. Pat. No. 5,389,133 (XEROX).

It is also possible to make mixtures of pigments. For example, in someinkjet ink application a neutral black inkjet ink is preferred and canbe obtained e.g. by mixing a black pigment and a cyan pigment into theink. Also pigments may be combined to enlarge the colour gamut of an inkset. The inkjet application may also require one or more spot colours.Silver and gold are often desired colours for making a product moreattractive by giving it an exclusive appearance.

Also non-organic pigments may be present in the inks. Suitable pigmentsare C.I. Pigment Metal 1, 2 and 3. Illustrative examples of theinorganic pigments include titanium oxide, barium sulfate, calciumcarbonate, zinc oxide, lead sulfate, yellow lead, zinc yellow, red ironoxide (III), cadmium red, ultramarine blue, prussian blue, chromiumoxide green, cobalt green, amber, titanium black and synthetic ironblack. However, care should be taken to prevent migration and extractionof heavy metals in food application. In the preferred embodiment nopigments are used which contain a heavy metal selected from the groupconsisting of arsenic, lead, mercury and cadmium.

Pigment particles in inkjet ink should be sufficiently small to permitfree flow of the ink through the inkjet-printing device, especially atthe ejecting nozzles. It is also desirable to use small particles formaximum colour strength and to slow down sedimentation.

The numeric average pigment particle size is preferably between 0.050and 1 μm, more preferably between 0.070 and 0.300 μm and particularlypreferably between 0.080 and 0.200 μm. Most preferably, the numericaverage pigment particle size is no larger than 0.150 μm. An averageparticle size smaller than 0.050 μm is less desirable for decreasedlight-fastness, but mainly also because very small pigment particles orindividual pigment molecules thereof may still be extracted in foodpackaging applications.

The numeric average pigment particle size of pigment particles is bestdetermined with a Brookhaven Instruments Particle Sizer BI90plus basedupon the principle of dynamic light scattering. The ink is then diluted,for example, with ethyl acetate to a pigment concentration of 0.002 wt%. The measurement settings of the BI90plus are: 5 runs at 23° C., angleof 90°, wavelength of 635 nm and graphics=correction function.

In the case of a white curable ink, preferably a pigment with arefractive index greater than 1.60, preferably greater than 2.00, morepreferably greater than 2.50 and most preferably greater than 2.60. Thewhite pigments may be employed singly or in combination.

Preferably titanium dioxide is used for the pigment with a refractiveindex greater than 1.60. Titanium oxide occurs in the crystalline formsof anatase type, rutile type and brookite type. The anatase type has arelatively low density and is easily ground into fine particles, whilethe rutile type has a relatively high refractive index, exhibiting ahigh covering power. Either one of these is usable in this invention. Itis preferred to make the most possible use of characteristics and tomake selections according to the use thereof. The use of the anatasetype having a low density and a small particle size can achieve superiordispersion stability, ink storage stability and ejectability. At leasttwo different crystalline forms may be used in combination. The combineduse of the anatase type and the rutile type which exhibits a highcoloring power can reduce the total amount of titanium oxide, leading toimproved storage stability and ejection performance of ink.

For surface treatment of the titanium oxide, an aqueous treatment or agas phase treatment is applied, and an alumina-silica treating agent isusually employed. Untreated-, alumina treated- or alumina-silicatreated-titanium oxide are employable.

The numeric average particle diameter of the titanium oxide or otherwhite pigments is preferably from 50 to 500 nm, more preferably from 150to 400 nm, and most preferably from 200 to 350 nm. Sufficient hidingpower cannot be obtained when the average diameter is less than 50 nm,and the storage ability and the jet-out suitability of the ink tend tobe degraded when the average diameter exceeds 500 nm. The determinationof the numeric average particle diameter is best performed by photoncorrelation spectroscopy at a wavelength of 633 nm with a 4 mW HeNelaser on a diluted sample of the pigmented inkjet ink. A suitableparticle size analyzer used was a MALVERN™ nano-S available fromGoffin-Meyvis. A sample can be, for example, be prepared by addition ofone drop of ink to a cuvet containing 1.5 mL ethyl acetate and mixeduntil a homogenous sample was obtained. The measured particle size isthe average value of 3 consecutive measurements consisting of 6 runs of20 seconds.

Generally pigments are stabilized in the dispersion medium by dispersingagents, such as polymeric dispersants or surfactants. However, thesurface of the pigments can be modified to obtain so-called“self-dispersible” or “self-dispersing” pigments, i.e. pigments that aredispersible in the dispersion medium without dispersants.

The pigment is preferably used in a pigment dispersion used forpreparing inkjet inks in an amount of 10 to 40 wt %, more preferably of15 to 30 wt % based on the total weight of the pigment dispersion. In acurable inkjet ink the pigment is preferably present in an amount of 0.1to 20 wt %, preferably 1 to 10 wt % based on the total weight of theinkjet ink.

Dispersants

The dispersant is preferably a polymeric dispersant. Typical polymericdispersants are copolymers of two monomers but may contain three, four,five or even more monomers. The properties of polymeric dispersantsdepend on both the nature of the monomers and their distribution in thepolymer. Suitable copolymeric dispersants have the following polymercompositions:

-   -   statistically polymerized monomers (e.g. monomers A and B        polymerized into ABBAABAB);    -   alternating polymerized monomers (e.g. monomers A and B        polymerized into ABABABAB);    -   gradient (tapered) polymerized monomers (e.g. monomers A and B        polymerized into AAABAABBABBB);    -   block copolymers (e.g. monomers A and B polymerized into        AAAAABBBBBB) wherein the block length of each of the blocks (2,        3, 4, 5 or even more) is important for the dispersion capability        of the polymeric dispersant;    -   graft copolymers (graft copolymers consist of a polymeric        backbone with polymeric side chains attached to the backbone);        and    -   mixed forms of these polymers, e.g. blocky gradient copolymers.

Polymeric dispersants may have different polymer architecture includinglinear, comb/branched, star, dendritic (including dendrimers andhyperbranched polymers). A general review on the architecture ofpolymers is given by ODIAN, George, Principles of Polymerization, 4thedition, Wiley-Interscience, 2004, p. 1-18.

Comb/branched polymers have side branches of linked monomer moleculesprotruding from various central branch points along the main polymerchain (at least 3 branch points).

Star polymers are branched polymers in which three or more eithersimilar or different linear homopolymers or copolymers are linkedtogether to a single core.

Dendritic polymers include the classes of dendrimers and hyperbranchedpolymers. In dendrimers, with well-defined mono-disperse structures, allbranch points are used (multi-step synthesis), while hyperbranchedpolymers have a plurality of branch points and multifunctional branchesthat lead to further branching with polymer growth (one-steppolymerization process).

Suitable polymeric dispersants may be prepared via addition orcondensation type polymerizations. Polymerization methods include thosedescribed by ODIAN, George, Principles of Polymerization, 4th edition,Wiley-Interscience, 2004, p. 39-606.

Addition polymerization methods include free radical polymerization(FRP) and controlled polymerization techniques.

Suitable controlled radical polymerization methods include:

-   -   RAFT: reversible addition-fragmentation chain transfer;    -   ATRP: atom transfer radical polymerization    -   MADIX: reversible addition-fragmentation chain transfer process,        using a transfer active xanthate;    -   Catalytic chain transfer (e.g. using cobalt complexes);    -   Nitroxide (e.g. TEMPO) mediated polymerizations;

Other suitable controlled polymerization methods include:

-   -   GTP: group transfer polymerization;    -   Living cationic (ring-opening) polymerizations;    -   Anionic co-ordination insertion ring-opening polymerization; and    -   Living anionic (ring-opening) polymerization.

Reversible addition-fragmentation transfer (RAFT): controlledpolymerization occurs via rapid chain transfer between growing polymerradicals and dormant polymer chains. A review article on RAFT synthesisof dispersants with different polymeric geometry is given in QUINN J. F.et al., Facile Synthesis of comb, star, and graft polymers viareversible addition-fragmentation chain transfer (RAFT) polymerization,Journal of Polymer Science, Part A: Polymer Chemistry, Vol. 40,2956-2966, 2002.

Group transfer polymerization (GTP): the method of GTP used forsynthesis of AB block copolymers is disclosed by SPINELLI, Harry J, GTPand its use in water based pigment dispersants and emulsion stabilisers,Proc. of 20th Int. Conf. Org. Coat. Sci. Technol., New Platz, N.Y.,State Univ. N.Y., Inst. Mater. Sci. p. 511-518.

The synthesis of dendritic polymers is described in the literature. Thesynthesis of dendrimers in NEWCOME, G. R., et al. Dendritic Molecules:Concepts, Synthesis, Perspectives. VCH: WEINHEIM, 2001. Hyperbranchingpolymerization is described by BURCHARD, W. Solution properties ofbranched macromolecules. Advances in Polymer Science. 1999, vol. 143,no. II, p. 113-194. Hyperbranched materials can be obtained bypolyfunctional polycondensation as disclosed by FLORY, P. J. Molecularsize distribution in three-dimensional polymers. VI. Branched polymercontaining A-R-Bf-1-type units. Journal of the American ChemicalSociety. 1952, vol. 74, p. 2718-1723.

Living cationic polymerizations is e.g. used for the synthesis ofpolyvinyl ethers as disclosed in WO 2005/012444 (CANON), US 20050197424(CANON) and US 20050176846 (CANON). Anionic co-ordination ring-openingpolymerization is e.g. used for the synthesis of polyesters based onlactones. Living anionic ring-opening polymerization is e.g. used forthe synthesis of polyethylene oxide macromonomers.

Free radical Polymerization (FRP) proceeds via a chain mechanism, whichbasically consists of four different types of reactions involving freeradicals: (1) radical generation from non-radical species (initiation),(2) radical addition to a substituted alkene (propagation), (3) atomtransfer and atom abstraction reactions (chain transfer and terminationby disproportionation), and (4) radical-radical recombination reactions(termination by combination).

Polymeric dispersants having several of the above polymer compositionsare disclosed in U.S. Pat. No. 6,022,908 (HP), U.S. Pat. No. 5,302,197(DU PONT) and U.S. Pat. No. 6,528,557 (XEROX).

Suitable statistical copolymeric dispersants are disclosed in U.S. Pat.No. 5,648,405 (DU PONT), U.S. Pat. No. 6,245,832 (FUJI XEROX), U.S. Pat.No. 6,262,207 (3M), US 20050004262 (KAO) and U.S. Pat. No. 6,852,777(KAO).

Suitable alternating copolymeric dispersants are described in US20030017271 (AKZO NOBEL).

Suitable block copolymeric dispersants have been described in numerouspatents, especially block copolymeric dispersants containing hydrophobicand hydrophilic blocks. For example, U.S. Pat. No. 5,859,113 (DU PONT)discloses AB block copolymers, U.S. Pat. No. 6,413,306 (DU PONT)discloses ABC block copolymers.

Suitable graft copolymeric dispersants are described in CA 2157361 (DUPONT) (hydrophobic polymeric backbone and hydrophilic side chains);other graft copolymeric dispersants are disclosed in U.S. Pat. No.6,652,634 (LEXMARK), U.S. Pat. No. 6,521,715 (DU PONT).

Suitable branched copolymeric dispersants are described U.S. Pat. No.6,005,023 (DU PONT), U.S. Pat. No. 6,031,019 (KAO), U.S. Pat. No.6,127,453 (KODAK).

Suitable dendritic copolymeric dispersants are described in e.g. U.S.Pat. No. 6,518,370 (3M), U.S. Pat. No. 6,258,896 (3M), US 2004102541(LEXMARK), U.S. Pat. No. 6,649,138 (QUANTUM DOT), US 2002256230 (BASF),EP 1351759 A (EFKA ADDITIVES) and EP 1295919 A (KODAK).

Suitable designs of polymeric dispersants for inkjet inks are disclosedin SPINELLI, Harry J., Polymeric Dispersants in Inkjet technology,Advanced Materials, 1998, Vol. 10, no. 15, p. 1215-1218.

The monomers and/or oligomers used to prepare the polymeric dispersantcan be any monomer and/or oligomer found in the Polymer Handbook Vol.1+2, 4th edition, edited by J. BRANDRUP et al., Wiley-Interscience,1999.

Polymers useful as pigment dispersants include naturally occurringpolymers, and specific examples thereof include: proteins, such as glue,gelatine, casein, and albumin; naturally occurring rubbers, such as gumarabic and tragacanth; glucosides such as saponin; alginic acid andalginic acid derivatives, such as propylene glycol alginate; andcellulose derivatives, such as methyl cellulose, carboxymethyl celluloseand ethylhydroxy cellulose; wool and silk, and synthetic polymers.

Suitable examples of monomers for synthesizing polymeric dispersantsinclude: acrylic acid, methacrylic acid, maleic acid (or there salts),maleic anhydride, alkyl(meth)acrylates (linear, branched and cycloalkyl)such as methyl(meth)acrylate, n-butyl(meth)acrylate,tert-butyl(meth)acrylate, cyclohexyl(meth)acrylate, and2-ethylhexyl(meth)acrylate; aryl(meth)acrylates such asbenzyl(meth)acrylate, and phenyl(meth)acrylate;hydroxyalkyl(meth)acrylates such as hydroxyethyl(meth)acrylate, andhydroxypropyl(meth)acrylate; (meth)acrylates with other types offunctionalities (e.g. oxiranes, amino, fluoro, polyethylene oxide,phosphate substituted) such as glycidyl (meth)acrylate,dimethylaminoethyl(meth)acrylate, trifluoroethyl acrylate,methoxypolyethyleneglycol (meth)acrylate, and tripropyleneglycol(meth)acrylate phosphate; allyl derivatives such as allyl glycidylether; styrenics such as styrene, 4-methylstyrene, 4-hydroxystyrene,4-acetostyrene, and styrene sulfonic acid; (meth)acrylonitrile;(meth)acrylamides (including N-mono and N,N-disubstituted) such asN-benzyl (meth)acrylamide; maleimides such as N-phenyl maleimide; vinylderivatives such as vinylcaprolactam, vinylpyrrolidone, vinylimidazole,vinylnapthalene, and vinyl halides; vinylethers such as vinylmethylether; vinylesters of carboxylic acids such as vinylacetate,vinylbutyrate, and vinyl benzoate.

Suitable condensation type polymers include polyurethanes, polyamides,polycarbonates, polyethers, polyureas, polyimines, polyimides,polyketones, polyesters, polysiloxanes, phenol-formaldehydes,urea-formaldehydes, melamine-formaldehydes, polysulfides, polyacetals orcombinations thereof.

Suitable copolymeric dispersants are acrylic acid/acrylonitrilecopolymers, vinyl acetate/acrylic ester copolymers, acrylic acid/acrylicester copolymers, styrene/acrylic acid copolymers, styrene/methacrylicacid copolymers, styrene/methacrylic acid/acrylic ester copolymers,styrene/α-methylstyrene/acrylic acid copolymers,styrene/α-methylstyrene/acrylic acid/acrylic ester copolymers,styrene/maleic acid copolymers, styrene/maleic anhydride copolymers,vinylnaphthalene/acrylic acid copolymers, vinylnapthalene/maleic acidcopolymers, vinyl acetate/ethylene copolymers, vinyl acetate/fattyacid/ethylene copolymers, vinyl acetate/maleic ester copolymers, vinylacetate/crotonic acid copolymers and vinyl acetate/acrylic acidcopolymers.

Suitable chemistries of copolymeric dispersants also include:

-   -   Copolymers which are the product of a condensation process of        poly(ethylene imine) with a carboxylic acid terminated polyester        (made by addition polymerization); and    -   Copolymers which are the product of a reaction of a        multifunctional isocyanate with:        -   a compound monosubstituted with a group that is capable of            reacting with an isocyanate, e.g. polyester;        -   a compound containing two groups capable of reacting with an            isocyanate (cross-linker); and/or        -   a compound with at least one basic ring nitrogen and a group            that is capable of reacting with an isocyanate group.

A detailed list of suitable polymeric dispersants is disclosed by MCCUTCHEON, Functional Materials, North American Edition, Glen Rock, N.J.:Manufacturing Confectioner Publishing Co., 1990, p. 110-129.

Suitable pigment stabilisers are also disclosed in DE 19636382 (BAYER),U.S. Pat. No. 5,720,802 (XEROX), U.S. Pat. No. 5,713,993 (DU PONT), WO96/12772 (XAAR) and U.S. Pat. No. 5,085,689 (BASF).

One polymeric dispersant or a mixture of two or more polymericdispersants may be present to improve the dispersion stability further.Sometimes surfactants can also be used as pigment dispersants, thus acombination of a polymeric dispersant with a surfactant is alsopossible.

The polymeric dispersant can be non-ionic, anionic or cationic innature; salts of the ionic dispersants can also be used.

The polymeric dispersant has preferably a polymerization degree DPbetween 5 and 1,000, more preferably between 10 and 500 and mostpreferably between 10 and 100.

The polymeric dispersant has preferably a number average molecularweight Mn between 500 and 30,000, more preferably between 1,500 and10,000.

The polymeric dispersant has preferably a weight average molecularweight Mw smaller than 100,000, more preferably smaller than 50,000 andmost preferably smaller than 30,000.

The polymeric dispersant has preferably a polymeric dispersity PDsmaller than 2, more preferably smaller than 1.75 and most preferablysmaller than 1.5.

Commercial examples of polymeric dispersants are the following:

-   -   DISPERBYK™ dispersants available from BYK CHEMIE GMBH;    -   SOLSPERSE™ dispersants available from NOVEON;    -   TEGO™ DISPERS™ dispersants from DEGUSSA;    -   EDAPLAN™ dispersants from MUNZING CHEMIE;    -   ETHACRYL™ dispersants from LYONDELL;    -   GANEX™ dispersants from ISP;    -   DISPEX™ and EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC;    -   DISPONER™ dispersants from DEUCHEM; and    -   JONCRYL™ dispersants from JOHNSON POLYMER.

Particularly preferred polymeric dispersants include SOLSPERSE™dispersants from NOVEON, EFKA™ dispersants from CIBA SPECIALTY CHEMICALSINC and DISPERBYK™ dispersants from BYK CHEMIE GMBH.

Particularly preferred dispersants for UV-curable pigmented dispersionsare SOLSPERSE™ 32000, 35000 and 39000 dispersants from NOVEON.

The polymeric dispersant is preferably used in an amount of 2 to 600 wt%, more preferably 5 to 200 wt % based on the weight of the pigment.

Inhibitors

The curable ink may contain a polymerization inhibitor. Suitablepolymerization inhibitors include phenol type antioxidants, hinderedamine light stabilizers, phosphor type antioxidants, hydroquinonemonomethyl ether commonly used in (meth)acrylate monomers, andhydroquinone, t-butylcatechol, pyrogallol,2,6-di-tert.butyl-4-methylphenol may also be used.

Suitable commercial inhibitors are, for example, SUMILIZER™ GA-80,SUMILIZER™ GM and SUMILIZER™ GS produced by Sumitomo Chemical Co. Ltd.;GENORAD™ 16, GENORAD™ 18 and GENORAD™ 20 from Rahn AG; IRGASTAB™ UV10and IRGASTAB™ UV22, TINUVIN™ 460 and CGS20 from Ciba SpecialtyChemicals; FLOORSTAB™ UV range (UV-1, UV-2, UV-5 and UV-8) fromKromachem Ltd, ADDITOL™ S range (S100, 5110, 5120 and 5130) from CytecSurface Specialties.

The inhibitor is preferably a polymerizable inhibitor.

In a preferred embodiment, the polymerizable inhibitor is apolymerizable phenolic polymerization inhibitor according to formula(II):

whereinR represents a hydrogen or a methyl group;X represents O or NR₁,m represents 0 or 1;n represents an integer from 1 to 5;o represents an integer from 1 to 6;A represents a substituted or unsubstituted phenolic moiety;L represents a (n+o)-valent linking group including at maximum 20 carbonatoms;R₁ represents a group selected from the group consisting of hydrogen, asubstituted or unsubstituted alkyl group, a substituted or unsubstitutedalkenyl group, a substituted or unsubstituted alkynyl group, asubstituted or unsubstituted aralkyl group, a substituted orunsubstituted alkaryl group, a substituted or unsubstituted aryl groupand a substituted or unsubstituted heteroaryl group.

In a preferred embodiment of the polymerizable phenolic polymerizationinhibitor according to formula (II), R represents hydrogen.

In a further preferred embodiment of the polymerizable phenolicpolymerization inhibitor according to Formula (II), n and o are equal to1.

In a particularly preferred embodiment of the polymerizable phenolicpolymerization inhibitor according to Formula (II), A is represented byFormula (III):

wherein the dotted line represents the bonding site of L or X to thecarbocyclic aromatic compound; andR₂ and R₃ are selected from the group consisting of a substituted orunsubstituted alkyl group, a substituted or unsubstituted alkenyl group,a substituted or unsubstituted alkynyl group, a substituted orunsubstituted aralkyl group, a substituted or unsubstituted alkarylgroup and a substituted or unsubstituted aryl group. Substituted orunsubstituted alkyl groups are particularly preferred.

In another particularly preferred embodiment of the polymerizablephenolic polymerization inhibitor according to Formula (II), A isrepresented by Formula (IV):

wherein the dotted line represents the bonding site of L or X to thecarbocyclic aromatic compound.

Typical examples of polymerizable phenolic polymerisation inhibitors,according to the present invention are given in Table 6, without beinglimited thereto.

TABLE 6 Stabilizer-1

Stabilizer-2

Stabilizer-3

Stabilizer-4

Stabilizer-5

Stabilizer-6

Stabilizer-7

Stabilizer-8

Stabilizer-9

Stabilizer-10

Stabilizer-11

Stabilizer-12

Stabilizer-13

Stabilizer-14

Stabilizer-15

Stabilizer-16

Since excessive addition of these polymerization inhibitors may lowerthe ink sensitivity to curing, it is preferred that the amount capableof preventing polymerization is determined prior to blending. The amountof a polymerization inhibitor is preferably lower than 5 wt %, morepreferably lower than 3 wt % of the total ink.

Surfactants

The surfactant(s) can be anionic, cationic, non-ionic, or zwitter-ionicand are usually added in a total quantity less than 20 wt % based on thetotal weight of the inkjet ink and particularly in a total less than 10wt % based on the total weight of the inkjet ink.

Suitable surfactants include fluorinated surfactants, fatty acid salts,ester salts of a higher alcohol, alkylbenzene sulphonate salts,sulphosuccinate ester salts and phosphate ester salts of a higheralcohol (for example, sodium dodecylbenzenesulphonate and sodiumdioctylsulphosuccinate), ethylene oxide adducts of a higher alcohol,ethylene oxide adducts of an alkylphenol, ethylene oxide adducts of apolyhydric alcohol fatty acid ester, and acetylene glycol and ethyleneoxide adducts thereof (for example, polyoxyethylene nonylphenyl ether,and SURFYNOL™ 104, 104H, 440, 465 and TG available from AIR PRODUCTS &CHEMICALS INC.).

For non-aqueous inkjet inks preferred surfactants are selected fromfluoro surfactants (such as fluorinated hydrocarbons) and siliconesurfactants. The silicones are typically siloxanes and can bealkoxylated, polyether modified, polyether modified hydroxy functional,amine modified, epoxy modified and other modifications or combinationsthereof. Preferred siloxanes are polymeric, for examplepolydimethylsiloxanes.

In radiation curable inkjet inks a fluorinated or silicone compound maybe used as a surfactant, however, a cross-linkable surfactant would bepreferred. It is therefore preferred to use a copolymerizable monomerhaving surface-active effects, for example, polyacrylate copolymers,silicone modified acrylates, silicone modified methacrylates, acrylatedsiloxanes, polyether modified acrylic modified siloxanes, fluorinatedacrylates, and fluorinated methacrylates; these acrylates can bemono-,di-, tri- or higher functional (meth)acrylates.

Surfactants are known for use in inkjet inks to reduce the surfacetension of the ink and to reduce the contact angle on the substrate,i.e. to improve the wetting of the substrate by the ink. On the otherhand, the jettable fluid must meet stringent performance criteria inorder to be adequately jettable with high precision, reliability andduring an extended period of time. To achieve both wetting of thesubstrate by the ink and high jetting performance, typically, thesurface tension of the ink is reduced by the addition of one or moresurfactants. In the case of curable inkjet inks, however, the surfacetension of the inkjet ink is not only determined by the amount and typeof surfactant, but also by the polymerizable compounds, the polymericdispersants and other additives in the ink composition.

Depending upon the application a surfactant can be used with a high, lowor intermediate dynamic surface tension. Silicone surfactants aregenerally known to have low dynamic surface tensions while fluorinatedsurfactants are known to have higher dynamic surface tensions.

Useful commercially available fluorinated surfactants are for examplethe ZONYL™ range of fluoro-surfactants from DUPONT and the FLUORAD™range of fluoro-surfactants from 3M. Other fluorinated surfactants aree.g. described in EP 1412438 A (3M).

Silicone surfactants are often preferred in curable inkjet inks,especially the reactive silicone surfactants, which are able to bepolymerized together with the polymerizable compounds during the curingstep.

Useful commercially available silicone surfactants are oftenpolysiloxane surfactants, especially polyether modified polysiloxanes,preferably with one or more acrylate function in order to becomepolymerizable.

Examples of useful commercial silicone surfactants are those supplied byBYK CHEMIE GMBH (including BYK™-302, 307, 310, 331, 333, 341, 345, 346,347, 348, UV3500, UV3510 and UV3530), those supplied by TEGO CHEMIESERVICE (including TEGO RAD™ 2100, 2200N, 2250, 2300, 2500, 2600 and2700), EBECRYL™ 350 a polysilixone diacrylate and EBECRYL™ 1360 apolysilixone hexaacrylate from CYTEC INDUSTRIES BV and Efka™-3000 series(including EFKA™-3232 and EFKA™-3883) from EFKA CHEMICALS B.V.

Inkjet Printing Methods

The inkjet printing method according to a preferred embodiment of thepresent invention includes the step of applying a layer having acomposition as defined above for the curable liquid or ink on asubstrate.

In a preferred embodiment of the inkjet printing method, the appliedlayer is a white primer, preferably containing a titanium dioxidepigment. White primers can be advantageously used, for example, ontransparent substrates to enhance the contrast and the vividness ofcolour inks. White curable inks are then either used for so-called“surface printing” or “backing printing” to form a reflection image on atransparent substrate. In surface printing, a white background is formedon a transparent substrate using a white ink and further thereon, acolor image is printed, where after the formed final image is viewedfrom the printed face. In so-called backing printing, a color image isformed on a transparent substrate using color inks and then a white inkis applied onto the color inks, and the final formed image is observedthrough the transparent substrate. In a preferred embodiment a colourinkjet ink is jetted on partially cured white inkjet ink. If the whiteink is only partially cured, an improved wettability of the colour inkon the white ink layer is observed. Partially curing immobilizes the inkon the substrate surface. A quick test to verify that the white inkjetink is partially cured can be done by rubbing a finger or a cloth acrossthe printed surface, whereby it is observed that ink can be smeared orsmudged on the surface.

In another preferred embodiment of the inkjet printing method, theapplied layer is a colourless layer. This layer can be present as aprimer, for example, for improving the adhesion of the image, or as anoutermost layer, for example, for improving the glossiness of the image.

The above layer is preferably applied by a printing technique selectedfrom the group consisting of inkjet printing, flexographic printing,offset printing and screen printing.

Alternatively, above layer is applied by a coating technique selectedfrom the group consisting of dip coating, knife coating, extrusioncoating, spin coating, slide hopper coating and curtain coating.

Inkjet Printing Device

Curable liquids and inks according to preferred embodiments of thepresent invention may be jetted by one or more printing heads ejectingsmall droplets of ink in a controlled manner through nozzles onto anink-receiver surface, which is moving relative to the printing head(s).

A preferred printing head for the inkjet printing system is apiezoelectric head. Piezoelectric inkjet printing is based on themovement of a piezoelectric ceramic transducer when a voltage is appliedthereto. The application of a voltage changes the shape of thepiezoelectric ceramic transducer in the printing head creating a void,which is then filled with ink. When the voltage is again removed, theceramic expands to its original shape, ejecting a drop of ink from theprint head. However the inkjet printing method according to the presentinvention is not restricted to piezoelectric inkjet printing. Otherinkjet printing heads can be used and include various types, such as acontinuous type and thermal, electrostatic and acoustic drop on demandtype.

At high printing speeds, the inks must be ejected readily from theprinting heads, which puts a number of constraints on the physicalproperties of the ink, e.g. a low viscosity at the jetting temperature,which may vary from 25° C. to 110° C., a surface energy such that theprinting head nozzle can form the necessary small droplets, a homogenousink capable of rapid conversion to a dry printed area, . . . .

The inkjet printing head normally scans back and forth in a transversaldirection across the moving ink-receiver surface. Often the inkjet printhead does not print on the way back. Bi-directional printing ispreferred for obtaining a high areal throughput. Another preferredprinting method is by a “single pass printing process”, which can beperformed by using page wide inkjet printing heads or multiple staggeredinkjet printing heads which cover the entire width of the ink-receiversurface. In a single pass printing process the inkjet printing headsusually remain stationary and the ink-receiver surface is transportedunder the inkjet printing heads.

Curing Device

Curable liquids and inks according to preferred embodiments of thepresent invention can be cured by exposing them to actinic radiation, bythermal curing and/or by electron beam curing. Curable liquids and inksincluding a diffusion hindered photoinitiator are preferably cured byradiation curing, more preferably by ultraviolet radiation. Curableliquids and inks including no initiator are cured by electron beamcuring.

The curing device may be arranged in combination with the print head ofthe inkjet printer, travelling therewith so that the curable liquid isexposed to curing radiation very shortly after been jetted.

In such an arrangement it can be difficult to provide a small enoughradiation source connected to and travelling with the print head.Therefore, a static fixed radiation source may be employed, e.g. asource of curing UV-light, connected to the radiation source by means offlexible radiation conductors such as a fibre optic bundle or aninternally reflective flexible tube.

Alternatively, the actinic radiation may be supplied from a fixed sourceto the radiation head by an arrangement of mirrors including a mirrorupon the radiation head.

The source of radiation arranged not to move with the print head, mayalso be an elongated radiation source extending transversely across theink-receiver surface to be cured and adjacent the transverse path of theprint head so that the subsequent rows of images formed by the printhead are passed, stepwise or continually, beneath that radiation source.

Any ultraviolet light source, as long as part of the emitted light canbe absorbed by the photo-initiator or photo-initiator system, may beemployed as a radiation source, such as, a high or low pressure mercurylamp, a cold cathode tube, a black light, an ultraviolet LED, anultraviolet laser, and a flash light. Of these, the preferred source isone exhibiting a relatively long wavelength UV-contribution having adominant wavelength of 300-400 nm. Specifically, a UV-A light source ispreferred due to the reduced light scattering therewith resulting inmore efficient interior curing.

UV radiation is generally classed as UV-A, UV-B, and

UV-C as follows:

UV-A: 400 nm to 320 nm

UV-B: 320 nm to 290 nm

UV-C: 290 nm to 100 nm.

Furthermore, it is possible to cure the image using, consecutively orsimultaneously, two light sources of differing wavelength orilluminance. For example, the first UV-source can be selected to be richin UV-C, in particular in the range of 260 nm-200 nm. The secondUV-source can then be rich in UV-A, e.g. a gallium-doped lamp, or adifferent lamp high in both UV-A and UV-B. The use of two UV-sources hasbeen found to have advantages e.g. a fast curing speed.

For facilitating curing, the inkjet printer often includes one or moreoxygen depletion units. The oxygen depletion units place a blanket ofnitrogen or other relatively inert gas (e.g. CO₂), with adjustableposition and adjustable inert gas concentration, in order to reduce theoxygen concentration in the curing environment. Residual oxygen levelsare usually maintained as low as 200 ppm, but are generally in the rangeof 200 ppm to 1200 ppm.

Thermal curing can be performed image-wise by use of a thermal head, aheat stylus, hot stamping, a laser beam, etc. If a laser beam is used,then preferably an infrared laser is used in combination with aninfrared dye in the curable ink.

When electron beams are employed, the exposure amount of the aforesaidelectron beam is preferably controlled to be in the range of 0.1-20Mrad. An exposure amount of not less than 0.1 Mrad does not result insufficient curing of the curable liquids and inks. An exposure amount ofat not more than 20 Mrad is not preferred because it is able to avoiddeteriorating deteriorate supports, especially paper and certain type ofplastics. Accepted as electron beam exposure systems are, for example, ascanning system, a curtain beam system, and a broad beam system.Appropriate acceleration voltage during electron beam exposure is100-300 kV. The most important advantage of using an electron beamexposure system, compared to the ultraviolet radiation exposure, is thatfor printing on toys and food packaging materials curable liquids andinks lacking an initiator can be used. Hence, no toxicological problemscan occur due to extraction of the initiator.

Preparation of Curable Inks

The average particle size and distribution is an important feature forinkjet inks. The inkjet ink may be prepared by precipitating or millingthe pigment in the dispersion medium in the presence of the dispersant.

Mixing apparatuses may include a pressure kneader, an open kneader, aplanetary mixer, a dissolver, and a Dalton Universal Mixer. Suitablemilling and dispersion apparatuses are a ball mill, a pearl mill, acolloid mill, a high-speed disperser, double rollers, a bead mill, apaint conditioner, and triple rollers. The dispersions may also beprepared using ultrasonic energy.

Many different types of materials may be used as milling media, such asglasses, ceramics, metals, and plastics. In a preferred embodiment, thegrinding media can include particles, preferably substantially sphericalin shape, e.g. beads consisting essentially of a polymeric resin oryttrium stabilized zirconium oxide beads.

In the process of mixing, milling and dispersion, each process isperformed with cooling to prevent build up of heat, and as much aspossible under light conditions in which actinic radiation has beensubstantially excluded.

The inkjet ink may contain more than one pigment, and may be preparedusing separate dispersions for each pigment, or alternatively severalpigments may be mixed and co-milled in preparing the dispersion.

The dispersion process can be carried out in a continuous, batch orsemi-batch mode.

The preferred amounts and ratios of the ingredients of the mill grindwill vary widely depending upon the specific materials and the intendedapplications. The contents of the milling mixture include the mill grindand the milling media. The mill grind includes pigment, polymericdispersant and a liquid carrier. For inkjet inks, the pigment is usuallypresent in the mill grind at 1 to 50 wt %, excluding the milling media.The weight ratio of pigment over polymeric dispersant is 20:1 to 1:2.

The milling time can vary widely and depends upon the pigment,mechanical device and residence conditions selected, the initial anddesired final particle size, etc. In a preferred embodiment of thepresent invention pigment dispersions with an average particle size ofless than 100 nm may be prepared.

After milling is completed, the milling media is separated from themilled particulate product (in either a dry or liquid dispersion form)using conventional separation techniques, such as by filtration, sievingthrough a mesh screen, and the like. Often the sieve is built into themill, e.g. for a bead mill. The milled pigment concentrate is preferablyseparated from the milling media by filtration.

In general it is desirable to make the inkjet inks in the form of aconcentrated mill grind, which is subsequently diluted to theappropriate concentration for use in the inkjet printing system. Thistechnique permits preparation of a greater quantity of pigmented inkfrom the equipment. By dilution, the inkjet ink is adjusted to thedesired viscosity, surface tension, colour, hue, saturation density, andprint area coverage for the particular application.

EXAMPLES Materials

All materials used in the following examples were readily available fromstandard sources such as Aldrich Chemical Co. (Belgium) and Acros(Belgium) unless otherwise specified. The water used was deionizedwater.

RT355D is an abbreviation for CINQUASIA™ Magenta RT-355-D, aquinacridone pigment, available from CIBA SPECIALTY CHEMICALS.

PY150 is an abbreviation used for CHROMOPHTAL™ Yellow LA2, a C.I.Pigment Yellow 150 pigment from CIBA SPECIALTY CHEMICALS.

PY150-2 is an abbreviation used for Yellow Pigment E4GN-GT, a C.I.Pigment Yellow 150 pigment from LANXESS.

PB15:4 is an abbreviation used for HOSTAPERM™ Blue P-BFS, a C.I. PigmentBlue 15:4 pigment from Clariant.

S35000 is an abbreviation used for SOLSPERSE™ 35000, apolyethyleneimine-polyester hyperdispersant from NOVEON.

S39000 is an abbreviation used for SOLSPERSE™ 39000, apolyethyleneimine-polyester hyperdispersant from NOVEON.

S35000-SOL is a 30% solution of 535000 in VEEA.

S39000-SOL is a 30% solution of 539000 in VEEA.

DB162 is an abbreviation used for the polymeric dispersant DISPERBYK™162 available from BYK CHEMIE GMBH whereof the solvent mixture of2-methoxy-1-methylethylacetate, xylene and n-butylacetate was removed.

VEEA is 2-(vinylethoxy)ethyl acrylate, a difunctional monomer availablefrom NIPPON SHOKUBAI, Japan.

DPGDA is dipropyleneglycoldiacrylate from SARTOMER.

SR489 is tridecyl acrylate from SARTOMER.

M600 is dipentaerythritol hexaacrylate and an abbreviation for MIRAMER™M600 available from RAHN AG.

M4004 is pentaerythritol ethoxylated tetraacrylate (PPTTA) availablefrom RAHN AG.

SR399LV is a low viscosity dipentaerythritol pentaacrylate and anabbreviation for SARTOMER™ 399LV available from SARTOMER.

MVE is ethyleneglycol monovinylether available from BASF.

DVE is thriethyleneglycol divinylether available from BASF.

MMA is N-decylmethacrylate available from ABCR GMBH.

DMA is tetraethyleneglycol dimethacrylate and an abbreviation forSARTOMER™ 209 available from SARTOMER.

DAET is Bis(b-allyloxyethyl)ether available from PFALTZ & BAUER.

DAES is diallyl succinate available from ALDRICH.

SR256 is 2-(2-ethoxy ethoxy)ethyl acrylate and an abbreviation forSARTOMER™ SR256 available from SARTOMER.

Acryloyloxyethyl succinate available from ALDRICH.

IRGACURE™ 127 is2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one,a photoinitiator available from CIBA SPECIALTY CHEMICALS.

DAROCUR™ ITX is 2-isopropyl isothioxanthone, a photo-initiator availablefrom CIBA SPECIALTY CHEMICALS.

DAROCUR™ 1173 is 2-hydroxy-2-methylpropiophenone, a photo-initiatoravailable from CIBA SPECIALTY CHEMICALS.

KIP150 is oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone]and an abbreviation for ESACURE™ KIP150 available from LAMBERTI.

GENOPOL™ TX1 is a polymeric thioxanthone derivative, useful as aphotoinitiator, available from RAHN AG.

GENOPOL™ AB1 is a polymeric aminobenzoate derivate, useful as asynergist for UV-curable compositions, available from RAHN AG.

Tegosol is a 1 wt % solution of TEGO™ Rad 2100 in VEEA, TEGO™ Rad 2100is a surfactant available from TEGO CHEMIE SERVICES GMBH.

Byksol is a 1 wt % solution of BYK™-333 in VEEA, BYK™-333 is asurfactant available from BYK CHEMIE GMBH.

BHT is an abbreviation for 2,6-di-tert.butyl-4-methylphenol, availablefrom ALDRICH CHEMICAL CO.

MPH is an abbreviation for 4-methoxyphenol, available from ALDRICHCHEMICAL CO.

GENORAD™ 16 is a polymerization inhibitor from RAHN AG.

PET100 is an 100 μm unsubbed PET substrate with on the backside anantiblocking layer with antistatic properties available fromAGFA-GEVAERT N.V. as P100C PLAIN/ABAS.

Measurement Methods

1. TDE-Level

The TDE-level represents the amount of volatile extractables by thermaldesorption. The amount of volatile extractables is determined on fullycured coatings by direct thermal desorption method, i.e. without samplepreparation. The fully cured coating on a PET100 substrate having abacking layer was analysed with a GERSTEL™ TDS2 ThermoDesorption Systemfrom Gerstel Gmbh & Co. KG using as operation conditions: 1.54 cm² ofthe cured coating was analyzed during 10 minutes at 150° C. with on-lineGC evaluation of peak intensity for the desorbed components. The ovenprogram was set to 40° C. for 30 seconds, followed by a temperatureincrease at a rate of 15° C./minute until 300° C., and keeping thesample at 300° C. for 5 minutes. The chromatographic column was a Db1column from J&W (30 m×0.32 mm, 1 μm film thickness); the carrier gas wasHe at a flow rate of 2 mL/min. The desorbed compounds were trapped onTenaxTA at −60° C.

The back coating on the PET100 substrate contained volatile compounds,including NMP. The amount of NMP detected was used as an internalstandard to calculate the amount of volatile compounds from the curedcoating expressed in ppm (μg extractable compound per g of curableliquid). The amount of volatile compounds of the cured coating isobtained by subtraction of the amount of volatile compounds of thePET100 substrate from the total amount of volatile compounds of curedcoating and PET100 substrate. This amount is very much depending uponthe composition of the curable liquid. The evaluation scale used for theexamples is given by Table 7.

TABLE 7 Total amount of desorbed components from the cured coatingEvaluation >5,000 ppm bad >3,000 ppm poor 1,000-3,000 ppm acceptable<1,000 ppm good <500 ppm very good3. Smell

The smell was evaluated by a panel of three persons by their nose.

4. Curing Degree

The curing degree is tested on a coating immediately after curing withUV light. The cured coating is rubbed with the means of a Qtip. When thesurface is not damaged, the coating is fully cured. When some of thecured coating can be damaged, the coating is only partly cured. When thewhole cured coating is damaged, the coating is not cured.

5. Viscosity

The viscosity of the formulations was measured using a Brookfield DV-II+viscometer at 25° C. at 3 rotations per minute (RPM) using a CPE 40spindle. A viscosity of less than 50 mPa·s was regarded to be suitablefor inkjet printing.

6. Brittleness

The brittleness is tested on a coating after full curing of the coatingwith UV light under nitrogen inerting atmosphere. The curablecomposition is coated on a clear PET film. After curing, the curedcoating is bended. Brittle layers peel off in parts from the support,while flexible coatings remain undamaged.

7. Average Particle Size

The average particle size of the pigment dispersions was determined byphoton correlation spectroscopy at a wavelength of 633 nm with a 4 mWHeNe laser on a diluted sample of the pigment dispersion. The particlesize analyzer used was a MALVERN™ Nano-S available from Goffin-Meyvis.

The sample was prepared by addition of one drop of dispersion to a cuvetcontaining 1.5 mL ethyl acetate and mixed until a homogenous sample wasobtained. The measured particle size is the average value of 3consecutive measurements consisting of 6 runs of 20 seconds.

8. Stability of the Curable Composition

The stability of the curable composition was evaluated by comparing theviscosity of the freshly prepared composition and the viscosity after aheat treatment of 6 days at 83° C. Very unstable compositions becomesolid upon this heat treatment. Very stable compositions have aviscosity which has an increase in viscosity limited to 25% of the freshcomposition. Since, this is a very severe test, compositions areconsidered to be stable when the formulation is not solidified at all(not even partly) after the heat treatment.

Example 1

This example illustrates the synthesis of polymerizable compounds Asuitable for curable inks in accordance with a preferred embodiment ofthe present invention. Examples are given for different types ofpolymerizable compounds.

Polymerizable Compound PC-1

The synthesis of the allyl ester acrylate compound PC-1 proceededaccording to the following scheme:

30 g (0.14 mol) of acryloyloxyethyl succinate was dissolved in 150 mL ofacetone. 28 mL (0.16 mol) of diisopropyl ethyl amine and 20 mg of BHTwere added. 20 g (0.16 mol) of allyl bromide was added and the mixturewas refluxed for two hours. The solvent was removed under reducedpressure and the residue was redissolved in 200 mL of methylenechloride. The methylene chloride fraction was extracted twice with 150mL of 1 N NaOH, once with 150 mL water and twice with 150 mL of 1 N HCl.The organic fraction was dried over MgSO₄, 30 mg of BHT was added andthe solvent was removed under reduced pressure. PC-1 was purified on aMerck SVP D40-column (Si60 15-40 μm, 90 g) using a step gradient elutionfrom methylene chloride/hexane 30/70 to methylene chloride (15 minutesisocratic 30/70, immediately followed by 34 minutes 100% methylenechloride) using a flow rate of 40 mL/min. 10 mg BHT was added beforeevaporation of the eluent. 16.6 g of PC-1 was isolated.Polymerizable Compounds PC-2, PC-3 and PC-4

The allyl ether acrylates PC-2, PC-3 and PC-4 were all prepared in thesame manner according to the following scheme:

0.14 mol of the appropriate allyl ether (=compound AE) was dissolved in100 mL of methylene chloride. 29.3 mL (0.17 mol) of diisopropyl ethylamine in 30 mL of methylene chloride was added. A solution of 14.5 mL(15.93 g, 0.17 mol) acryloyl chloride in 20 mL of methylene chloride wasadded dropwise, while the temperature was kept between 10 and 20° C. Thereaction was allowed to continue for one and a half hour. The reactionmixture was extracted three times with 100 mL of 2N NaOH, once with 100mL water and two times with 100 mL of 2N HCl. The organic fraction wasdried over MgSO₄, 20 mg of BHT was added and the solvent was evaporatedunder reduced pressure.

For polymerizable compound PC-2, the compound AE (n=4) was preparedaccording to Perret-Aebi et al., Angewandte Chemie, InternationalEdition (2004), 43(34), 4482-4485. PC-2 was purified on a Merck SVPD40-column (Si60 15-40 μm, 90 g) using methylene chloride as eluent at aflow rate of 40 mL/min. 10 mg BHT was added before evaporation of theeluent. 17.25 g of polymerizable compound PC-2 was isolated.

For polymerizable compound PC-3, the compound AE (n=2) was availablefrom FLUKA. The polymerizable compound PC-3 was purified on a ProchromLC80-system, using Kromasil 60A 10 μm spherical silica. A gradientelution from 100% methylene chloride to methylene chloride/methanol95/5, over 26 minutes was used, at a flow rate of 150 mL/min. 10 mg BHTwas added before evaporation of the eluent.

For polymerizable compound PC-4, the compound AE (n=1) was availablefrom ALDRICH. The polymerizable compound PC-4 was purified on a MerckSVP D40-column (Si60 15-40 μm, 90 g) using a step gradient elution from100% methylene chloride to methylene chloride/methanol 99/1 (25 minisocratic elution with 100% methylene chloride, immediately followed byelution with methylene chloride/methanol 99/1). 10 mg BHT was addedbefore evaporation of the eluent.

Comparative Polymerizable Compounds

A comparative monomer CM-1 was synthesised according to the followingscheme:

Diethylene Glycol Monoacrylate:

25 g (0.235 mol) of diethylene glycol was dissolved in 150 mL of THF. 18mL of (0.13 mol) of triethyl amine was added, followed by the dropwiseaddition of 10.8 g (8 mL, 0.12 mol) of acryloyl chloride. The reactiontemperature was kept below 30° C. The reaction was allowed to continuefor 2 hours at room temperature. The precipitated triethyl aminehydrochloride was removed by filtration, 100 mg BHT was added and thesolvent was removed under reduced pressure. Diethylene glycolmonoacrylate was purified on a Prochrom LC80-system, using Kromasil 60A10 μm spherical silica. Methylene chloride/ethyl acetate 60/40 was usedas eluent at a flow rate of 200 mL/min. 10 mg BHT was added beforeevaporation of the eluent. 9.4 g of diethylene glycol monoacrylate wasisolated.

Comparative Monomer CM-1:

8.1 g (51 mmol) of diethylene glycol monoacrylate was dissolved in 40methylene chloride. 7.7 mL (55 mmol) of triethyl amine and 7.9 g (51mmol) of methacrylic anhydride were added. The reaction mixture wasrefluxed for 3 hours. The solvent was evaporated under reduced pressureand Comparative monomer-1 was purified on a Prochrom LC80-system, usingKromasil 60A 10 μm spherical silica. Methylene chloride/ethyl acetate93/7 was used as eluent at a flow rate of 200 mL/min. 10 mg BHT wasadded before evaporation of the eluent. 6.5 g of comparative monomerCM-1 was isolated.

Example 2

This example illustrates the influence of the weight percentages ofcompounds A, B and/or C in the polymerizable composition of the freeradical curable liquid.

Preparation of the Free Radical Curable Liquids

All free radical curable liquids COMP-1 to COMP-7 and INV-1 to INV-28were prepared in the same manner according to Table 8.

The preparation is exemplified for inventive liquid INV-10. LiquidINV-10 was prepared by mixing 58.50 g of VEEA, 9.75 g of DPGDA, 29.25 gof M600 and 2.50 g of INI-C1 as the polymerizable composition for 20minutes. Then 30 mg of BYK333 was added as a surfactant to thepolymerizable composition and the obtained free radical curable liquidwas stirred for 30 minutes. All prepared free radical curable liquidscontained 30 mg of BYK333 and 2.50 g of photoinitiator.

The compound INI-C1 is a polymerizable photoinitiator having oneacrylate group. Therefore, it has to be taken in to account as acompound B for calculating the weight percentages of the compounds A, Band C in the polymerizable composition of the free radical curableliquid. Table 8 shows the weight percentages of all other compounds A, Band/or C in the polymerizable composition, all based upon the totalweight of the polymerizable composition.

The polymerizable photoinitiator INI-C1 was prepared according to thesynthesis disclosed in Example 2 of DE 3534645 A (MERCK PATENT GMBH).

In a number of free radical curable liquids, for example, liquids COMP-1to COMP-5, the 2.50 g of polymerizable photoinitiator INI-C1 wasreplaced by 2.50 g of the non-polymerizable, duofunctionalphotoinitiator Irgacure™ 127 (=INI-A1 of Table 2). In these cases, thelast column of wt % INI-C1 in Table 8 remains empty.

TABLE 8 Compound A Compound B Compound C INI-C1 Liquid Type wt % Type wt% Type wt % wt % COMP-1 VEEA 3.05 DPGDA 96.95 — — — COMP-2 VEEA 27.29DPGDA 72.71 — — — COMP-3 VEEA 51.52 DPGDA 48.48 — — — COMP-4 VEEA 75.76DPGDA 24.24 — — — COMP-5 VEEA 41.05 SR489 58.95 — — — COMP-6 — — — —M600 97.50 2.50 COMP-7 VEEA 19.50 — — M600 78.00 2.50 INV-1 VEEA 100.00— — — — — INV-2 VEEA 78.32 SR489 21.68 — — — INV-3 VEEA 79.48 DPGDA20.52 — — — INV-4 VEEA 53.63 — — M4004 43.87 2.50 INV-5 VEEA 79.48 — —SR399LV 20.52 — INV-6 VEEA 79.48 — — M600 20.52 — INV-7 VEEA 77.49 — —M600 20.01 2.50 INV-8 VEEA 63.38 — — M600 34.12 2.50 INV-9 VEEA 48.75 —— M600 48.75 2.50 INV-10 VEEA 58.50 DPGDA 9.75 M600 29.25 2.50 INV-11VEEA 58.51 DPGDA 34.12 M600 4.87 2.50 INV-12 VEEA 58.50 DPGDA 37.05 M6001.95 2.50 INV-13 VEEA 41.26 DPGDA 38.22 M600 20.52 — INV-14 VEEA 39.00DPGDA 29.25 M600 29.25 2.50 INV-15 VEEA 39.00 DPGDA 48.75 M600 9.75 2.50INV-16 VEEA 29.25 DPGDA 51.19 M600 17.06 2.50 INV-17 VEEA 58.51 DPGDA34.12 M4004 4.87 2.50 INV-18 VEEA 24.38 SR489 53.62 M600 19.50 2.50INV-19 PC-4 76.43 — — M600 20.52 — VEEA 3.05 INV-20 PC-4 48.75 — — — —2.50 VEEA 48.75 INV-21 PC-4 48.75 — — M600 48.75 2.50 INV-22 PC-4 63.38— — M600 34.12 2.50 INV-23 PC-4 58.50 DPGDA 34.12 M600 4.88 2.50 INV-24PC-1 76.43 — — M600 20.52 — VEEA 3.05 INV-25 PC-1 48.75 DPGDA 48.75 — —2.50 INV-26 PC-1 48.75 — — M600 48.75 2.50 INV-27 PC-1 63.38 — — M60034.12 2.50 INV-28 PC-1 39.00 DPGDA 48.75 M600 9.75 2.50Preparation and Evaluation of Cured Samples

The free radical curable liquids COMP-1 to COMP-7 and INV-1 to INV-28were coated on a PET100 substrate using a bar coater and a 10 μm wiredbar. Each coated sample was cured using a Fusion DRSE-120 conveyer,equipped with a Fusion VPS/1600 lamp (D-bulb), which transported thesamples twice under the UV-lamp on a conveyer belt at a speed of 10m/min. The samples were cured under nitrogen inerting conditions. Beforea coated sample was placed on the conveyer belt, the coated sample wasmounted on a metal plate and on top of the plate a metal frame of 1 cmheight with a non UV-absorbing quartz glass window was placed, so that asealed chamber was formed with the coated sample inside. Then, thetrapped air in the chamber was replaced by nitrogen gas by introducingpure nitrogen gas into the chamber for 30 seconds.

All cured samples were found to be fully cured. Each of the curedsamples COMP-1 to COMP-7 and INV-1 to INV-28 were then evaluated ontheir amount of volatile extractables and their brittleness.

The difference between cured samples having high or low amounts ofvolatile extractables by thermal desorption is immediately apparent fromthe obtained thermal desorption chromatograms as illustrated in theFIGURE. The top chromatogram “blank” is the thermal desorptionchromatogram of the PET100 substrate possessing a backlayer, the middlechromatogram “sample-1” represents the chromatogram obtained for thecured sample of the liquid INV-6 and the bottom chromatogram “sample-2”represents the chromatogram obtained for the cured sample of the liquidCOMP-6.

All the results are shown by Table 9.

TABLE 9 Brittleness Cured sample of TDE-level Viscosity cured ink COMP-1bad OK OK COMP-2 bad OK OK COMP-3 bad OK OK COMP-4 poor OK OK COMP-5poor OK OK COMP-6 very good too high very brittle COMP-7 poor too highvery brittle INV-1 very good OK OK INV-2 good OK OK INV-3 good OK OKINV-4 very good OK OK INV-5 very good OK OK INV-6 very good OK OK INV-7very good OK OK INV-8 good OK OK INV-9 good OK OK INV-10 very good OK OKINV-11 very good OK OK INV-12 very good OK OK INV-13 good OK OK INV-14very good OK OK INV-15 very good OK OK INV-16 very good OK OK INV-17very good OK OK INV-18 very good OK OK INV-19 very good OK OK INV-20good OK OK INV-21 very good OK OK INV-22 very good OK OK INV-23 verygood OK OK INV-24 good OK OK INV-25 good OK OK INV-26 very good OK OKINV-27 very good OK OK INV-28 good OK OK

From Table 9, it should be clear that the weight percentages ofcompounds A, B and/or C in the polymerizable composition of the freeradical curable liquid determine the amount of volatile extractableseven when diffusion hindered photoinitiators are used and no othervolatile compounds are present.

Example 3

This example illustrates that the addition of a large amount ofpolymerizable compound not falling under the definition of compounds A,B or C does not lead to curable liquids exhibiting a low amount ofextractables after curing.

Preparation of the Free Radical Curable Liquids

All free radical curable liquids COMP-8 to COMP-11 and INV-29 wereprepared in the same manner by mixing 67.0 g of VEEA, 20.0 g of a secondmonomer according to Table 10, 2.5 g of IRGACURE™ 127, 2.5 g of GENOPOL™TX1, 5.0 g of GENOPOL™ AB1 and 3.0 g of BYKSOL. The free radical curableliquid was stirred for 30 minutes.

The polymerizable composition of the free radical curable liquids COMP-8to COMP-11 and INV-29 consisted of 77.8 wt % of Compound A (VEEA) and22.2 wt % of the second monomer based upon the total weight of thepolymerizable composition.

Preparation and Evaluation of Cured Samples

Fully cured samples of the free radical curable liquids COMP-8 toCOMP-11 and INV-29 were prepared in exactly the same manner as disclosedby EXAMPLE 2.

The amount of volatile extractables by thermal desorption was determinedand is shown in Table 10.

TABLE 10 Cured Second TDE- samples of monomer level COMP-8 MVE badCOMP-9 DVE bad COMP-10 MMA bad COMP-11 DMA bad INV-29 SR399LV good

Table 10 shows that replacement of SR399LV (compound C) by non-acrylatedvinylethers or methacrylates does no longer deliver a good TDE-level.

Example 4

This example illustrates that it is necessary that the polymerizablegroups G1 and G2 are part of the same polymerizable compound A, and thatthe polymerizable compound A cannot be replaced by two polymerizablecompounds, one having one or more G1-groups and the other one having oneor more G2 groups.

Preparation of the Free Radical Curable Liquids

All free radical curable liquids COMP-12 to COMP-15 were prepared in thesame manner as in EXAMPLE 3, but using the compounds according to Table11.

TABLE 11 wt % of compound COMP-12 COMP-13 COMP-14 COMP-15 SR256 37.2537.25 — — MVE 37.25 — — — DVE — 37.25 — — DPGDA — — 37.25 37.25 DAET — —37.25 — DAES — — — 37.25 SR399LV 20.00 20.00 — — M600 — — 20.00 20.00IRGACURE ™ 2.50 2.50 2.50 2.50 127 BYKSOL 3.00 3.00 3.00 3.00Preparation and Evaluation of Cured Samples

The coated samples of the free radical curable liquids COMP-12 toCOMP-15 were prepared and cured in the exactly the same manner asdisclosed by EXAMPLE 2.

The curing degree was determined for each of the cured samples of thefree radical curable liquids COMP-12 to COMP-15. Only the cured samplesof the free radical curable liquids COMP-13 and COMP-14 appeared to befully cured. However, the cured sample of COMP-13 exhibited a strongsmell. Therefore, only for the cured sample of COMP-14 was the amount ofvolatile extractables by thermal desorption determined.

TABLE 12 Cured Curing TDE- sample of Monomer 1 Monomer 2 degree levelCOMP-12 monoacrylate monovinylether partially — cured COMP-13 diacrylatedivinylether fully cured — COMP-14 diacrylate diallylether fully curedbad COMP-15 diacrylate diallylester partially — cured

The results in Table 12 can be best compared with the result obtainedwith liquid INV-5 in EXAMPLE 2 for the cured samples of COMP-12 andCOMP-13, with liquid INV-19 in EXAMPLE 2 for the cured sample of COMP-14and with liquid INV-24 in EXAMPLE 2 for the cured sample of COMP-15.

It should be clear from the results of COMP-12 and COMP-13 that thevinylether group and the acrylate group have to be present in the samemolecule. The same conclusion can be made for combining an acrylategroup and an allylether group in one molecule and for combining anacrylate group and an allylester group in one molecule.

Example 5

This example illustrates that the polymerizable compound A may containmore than one G1 and or G2 group.

Preparation of the Free Radical Curable Liquids

All free radical curable liquids COMP-16 to COMP-18 and INV-30 to INV-34were prepared in the same manner by mixing 74.5 g of a monomer Xaccording to Table 13, 20.0 g of M600, and 2.5 g of IRGACURE™ 127 and3.0 g of BYKSOL. The free radical curable liquids were stirred for 30minutes.

Preparation and Evaluation of Cured Samples

The coated samples of the free radical curable liquids COMP-16 toCOMP-18 and INV-30 to INV-34 were prepared and cured in the exactly thesame manner as disclosed by EXAMPLE 2.

The curing degree was determined for each of the cured samples. Only thecured samples of the free radical curable liquids COMP-17 and COMP-18could not or only partially fully cured and therefore the amount ofvolatile extractables by thermal desorption was determined. The resultsare shown in Table 13.

TABLE 13 # Cured Monomer Acrylate Other group(s) Curing TDE- sample of Xgroups Type # degree level COMP-16 DPGDA 2 — 0 fully bad cured COMP-17DAET 0 allylether 2 not cured — COMP-18 DAES 0 allylester 2 partially —cured INV-30 VEEA 1 vinylether 1 fully very cured good INV-31 PC-4 1allylether 1 fully very cured good INV-32 PC-1 1 allylether 1 fully goodcured INV-33 ADAE 1 allylether 2 fully good cured INV-34 DAAE 2allylether 1 fully very cured good

From Table 13, it should be clear that a low amount of volatileextractables was observed when the monomer fulfilled the requirements ofa polymerizable compound A according to a preferred embodiment of thepresent invention.

Example 6

This example illustrates the effect on the amounts of extractables aftercuring of the photoinitiator type used in the radiation curable liquids.

Preparation of the Free Radical Curable Liquids

All free radical curable liquids COMP-19 and COMP-20 and INV-35 toINV-42 were prepared in the same manner as in EXAMPLE 3, but using thecompounds according to Table 14 and Table 15.

TABLE 14 wt % of: COMP-19 COMP-20 INV-35 INV-36 INV-37 VEEA 74.50 74.5074.50 74.50 74.50 SR399LV 20.00 20.00 20.00 20.00 20.00 DAROCUR ™ 2.50 —— — — ITX DAROCUR ™ — 2.50 — — — 1173 IRGACURE ™ — — 2.50 — — 127 KIP150— — — 2.50 — INI-C1 — — — — 2.50 BYKSOL 3.00 3.00 3.00 3.00 3.00

TABLE 15 wt % of: INV-38 INV-39 INV-40 INV-41 INV-42 VEEA 72.00 67.0062.00 67.00 67.00 SR399LV 20.00 20.00 20.00 20.00 20.00 Irgacure ™ 2.502.50 2.50 — — 127 KIP150 — — — 5.00 2.50 INI-C1 — — — — 2.50 GENOPOL ™2.50 2.50 2.50 — — TX1 GENOPOL ™ — 5.00 — 5.00 5.00 AB1 COINI-1 — —10.00 — — BYKSOL 3.00 3.00 3.00 3.00 3.00Synthesis of Co-Initiator COINI-1

The synthesis was performed according to the following scheme:

14.2 g (0.215 mol) of 85% KOH was dissolved in 100 mL ethanol. Thetemperature rose to 30° C. 30 g (0.178 mol) of 4-dimethylamino benzoicacid was added and the mixture was stirred for 90 minutes. The solventwas evaporated under reduced pressure. The residue was treated with 300mL methyl tert. butyl ether, isolated by filtration and dried.

9.4 g (47 mmol) of 4-dimethylamino benzoic acid potassium salt was addedto a solution of 10 g (56 mmol) of 2-bromoethyl acrylate in 40 mLdimethyl acetamide. 1 g of BHT was added and the mixture was heated to60° C. for 2 hours. The reaction was allowed to cool down to roomtemperature. The formed potassium bromide was removed by filtration and150 mL of methyl tert. butyl ether was added. The mixture was extractedwith 150 mL of water. The organic fraction was isolated and dried overMgSO₄ and evaporated under reduced pressure. The residue was redissolvedin 150 mL of methyl tert. butyl ether and extracted with 150 mL of a 1 MNaHCO₃-solution. The organic layer was dried over MgSO₄ and evaporatedunder reduced pressure. The residue was treated with water. COINI-1precipitated from the medium, was isolated by filtration and dried. 4.3g of COINI-1 was isolated.

Preparation and Evaluation of Cured Samples

Only the cured sample of COMP-19 exhibited a strong smell. All othercured samples exhibited no or moderate smell and were evaluated fortheir amount of volatile extractables by thermal desorption. The resultsare shown in Table 16.

TABLE 16 Cured Curing sample of degree Smell TDE-level Viscosity COMP-19fully strong smell — OK cured COMP-20 fully moderate bad OK cured smellINV-35 fully no smell very good OK cured INV-36 fully moderate good OKcured smell INV-37 fully no smell very good OK cured INV-38 fully nosmell very good OK cured INV-39 fully no smell good OK cured INV-40fully no smell good OK cured INV-41 fully no smell good OK cured INV-42fully no smell very good OK cured

From Table 16, it is clear that a monofunctional photoinitiator exhibitsa large amount of volatile extractables by thermal desorption. Goodresults were obtained for duo- or polyfunctional photoinitiators andpolymeric photoinitiators, but especially with polymerizablephotoinitiators a very small amount of volatile extractables by thermaldesorption was observed.

Example 7

This example illustrates that the free radical polymerizable compositioncan be used to prepare free radical curable inkjet inks exhibiting lowamounts of extractables after curing.

Preparation of the Cyan Pigment Dispersion C1

A concentrated pigment dispersion C1 was prepared by mixing for 30minutes the components according to Table 17 in a 1000 mL vessel using aDISPERLUX™ YELLOW075 (from DISPERLUX S.A.R.L., Luxembourg). The vesselwas then connected to a EIGER™ Lab Bead mill (from EIGER TORRANCE Ltd.)having a bead filling of 52% with 0.4 mm yttrium stabilized zirconiumoxide beads (“high wear resistant zirconia grinding media” from TOSOHCo.) and milling for 100 minutes. After milling the dispersion wasseparated from the beads using a filter cloth.

TABLE 17 Component Quantity PB15:4 140.0 g S39000-SOL 466.7 g Genorad 16 14.0 g VEEA  79.3 g

The average particle size of the concentrated pigmented dispersions C1was 109 nm measured with the Malvern Nano-S.

Preparation of the Curable Inks

The comparative pigmented curable ink COMP-21 and the inventivepigmented curable inks INV-43 and INV-44 were prepared by adding to thecyan dispersion C1 the components according to Table 18. The weight %(wt %) of the components are based on the total weight of the curableink.

TABLE 18 wt % of: COMP-21 INV-43 INV-44 C1 15.00 15.00 15.00 VEEA 18.2659.50 59.50 SR399LV — 20.00 — M600 — — 20.00 SR256 61.24 — — IRGACURE ™2.50 2.50 2.50 127 Byksol 3.00 3.00 3.00Preparation and Evaluation of Cured Samples

Fully cured samples of the comparative pigmented curable ink COMP-21 andthe inventive pigmented curable inks INV-43 and INV-44 were prepared inexactly the same manner as disclosed by EXAMPLE 2.

The amount of volatile extractables by thermal desorption was determinedand is shown in Table 19.

TABLE 19 Cured sample of Curing degree Smell TDE-level COMP-21 fullycured strong smell bad INV-43 fully cured no smell good INV-44 fullycured no smell very good

From Table 19, it is clear that small amount of volatile extractables bythermal desorption were observed for free radical curable inkjet inks inaccordance with a preferred embodiment of the present invention.

Example 8

This example illustrates the synthesis of polymerizable inhibitors forfree radical polymerizable compositions fluids and inks in accordancewith the present invention.

Synthesis of Stabilizer-1: 2-methyl-propenoic acid2-[[(2-(4-hydroxy-phenoxy)-ethyl)amino]carbonyl]aminoethyl ester

N,N,O-tribenzyl-hydroquinone-mono(2-aminoethyl)-ether

25 g (84.4 mmol) N,N-dibenzyl-2-chloroethylamine hydrochloride and 34.5g (250 mmol) K₂CO₃ were refluxed in 320 mL acetonitrile. 17.25 g (84.6mmol) 4-benzyloxyphenol was added and the reaction mixture was refluxedfor 6 hours. The reaction mixture was allowed to cool down to roomtemperature and the precipitated salts were removed by filtration. Thesolvent was removed under reduced pressure. 36.1 g of the crudeN,N,O-tribenzyl-hydroquinone-mono(2-aminoethyl)-ether was isolated.N,N,O-tribenzyl-hydroquinone-mono(2-aminoethyl)-ether was purified usingpreparative column chromatography (Kieselgel 60, cyclohexane/ethylacetate: 20/1. 21.1 g (59%) ofN,N,O-tribenzyl-hydroquinone-mono(2-aminoethyl)-ether was isolated(m.p.: 45-47° C.)

Hydroquinone-mono(2-aminoethyl)ether chlorohydrate

25.6 g (60.7 mmol) N,N,O-tribenzyl-hydroquinone-mono(2-aminoethyl)-etherwas dissolved in hot ethanol. 7.7 mL concentrated hydrochloric acid and4.7 g Pd/C were added andN,N,O-tribenzyl-hydroquinone-mono(2-aminoethyl)-ether was hydrogenatedat 50° C. and under a pressure of 3 atmosphere. The catalyst was removedby filtration and washed with 50 mL ethanol. The solvent was removedunder reduced pressure. The residue was treated with 50 mL acetonitrile,isolated by filtration and dried under reduced pressure at 40° C. 9.8 g(85%) of hydroquinone-mono(2-aminoethyl)ether chlorohydrate was isolated(m.p.: 169-171° C.)

2-methyl-propenoic acid2-[[(2-(4-hydroxy-phenoxy)-ethyl)amino]carbonyl]aminoethyl ester

3 g (16 mmol) hydroquinone-mono(2-aminoethyl)ether chlorohydrate wasdissolved in 100 mL methylene chloride. 2.7 mL (19 mmol) triethyl aminewas added, followed by the addition of 2.9 mL (19 mmol)2-methyl-2-pronenoic acid-2-isocyanatoethyl ester. The reaction wasallowed to continue for 5 hours at room temperature. The reactionmixture was extracted with 100 mL of a 0.1 N HCl solution, dried overMgSO₄ and evaporated under reduced pressure. The crude2-methyl-propenoic acid2-[[(2-(4-hydroxy-phenoxy)-ethyl)amino]carbonyl]aminoethyl ester waspurified by preparative column chromatography on a Merck SVP D40 column,using a gradient elution from methylene chloride to methylenechloride/methanol 95/5. 2.4 g (49%) of 2-methyl-propenoic acid2-[[(2-(4-hydroxy-phenoxy)-ethyl)amino]carbonyl]aminoethyl ester wasisolated.

Synthesis of Stabilizer-2: of 2-methyl-propenoic acid2-[[(2-(4-hydroxy-3,5-di tert.butyl-phenyl)-methyl)amino]carbonyl]aminoethyl ester

3,5-di-tert.butyl-4-hydroxybenzaldehyde

20 g (91 mmol) 2,6-di-tert.butyl-4-methylphenol was dissolved in 1 ltert.butanol. 9.2 mL (28.9 g, 180 mmol) bromine was added drop wise atroom temperature. The reaction is allowed to continue at roomtemperature for 16 hours. 3,5-di-tert.butyl-4-hydroxybenzaldehydecrystallized from the medium. 3,5-di-tert.butyl-4-hydroxybenzaldehydewas isolated by filtration and dried. 7.82 g3,5-di-tert.butyl-4-hydroxybenzaldehyde was isolated. The filtrate wasconcentrated to 150 mL and a second crop crystallized from the medium.3,5-di-tert.butyl-4-hydroxybenzaldehyde was isolated by filtration anddried. 4.49 g 3,5-di-tert.butyl-4-hydroxybenzaldehyde was isolated. Thetwo fractions of 3,5-di-tert.butyl-4-hydroxybenzaldehyde were pooled and12.31 g (58%) 3,5-di-tert.butyl-4-hydroxybenzaldehyde was isolated(m.p.: 186-8° C.)

N-formyl-3,5-di-tert.butyl-4-hydroxybenzyl-amine: A mixture of 11.09 g(47 mmol) 3,5-di-tert.butyl-4-hydroxybenzaldehyde, 40 g ammonium formateand 40 mL formamide were stirred and heated to 170° C. for 30 minutes.The mixture was allowed to cool down to room temperature and treatedwith 100 mL water. The crudeN-formyl-3,5-di-tert.butyl-4-hydroxybenzyl-amine precipitated from themixture, was isolated by filtration, washed with water and dried. Thecrude N-formyl-3,5-di-tert.butyl-4-hydroxybenzyl-amine wasrecrystallized from toluene/heptane 1/1. 9.36 g (76%) ofN-formyl-3,5-di-tert.butyl-4-hydroxybenzyl-amine was isolated (130-1°C.)

3,5-di-tert.butyl-4-hydroxybenzyl amine

9.81 g (37.3 mmol) N-formyl-3,5-di-tert.butyl-4-hydroxybenzyl-amine wasdissolved in 24 mL dioxane and 7.2 mL concentrated hydrochloric acid.The mixture was heated to reflux for one hour. The mixture was allowedto cool down to room temperature and diluted with 50 mL water. Themixture was made alkaline, using a 10% ammonia solution.3,5-di-tert.butyl-4-hydroxybenzyl amine precipitated from the medium,was isolated by filtration and dried. 8.5 g (97%) of3,5-di-tert.butyl-4-hydroxybenzyl amine was isolated (m.p.: 159-9° C.).3,5-di-tert.butyl-4-hydroxybenzyl amine has a tendency to lose ammoniaupon heating, forming the corresponding di- and tribenzyl derivatives.

2-methyl-propenoic acid 2-[[(2-(4-hydroxy-3,5-di tert.butyl-phenyl)-methyl)amino]carbonyl]aminoethyl ester

4 g (17 mmol) 3,5-di-tert.butyl-4-hydroxybenzyl amine was dissolved in90 mL methylene chloride. 10 mg BHT was added, followed by the additionof 2.5 mL (17 mmol) 2-methyl-2-pronenoic acid-2-isocyanatoethyl ester.The reaction was allowed to continue for 30 minutes at room temperature.The solvent was removed under reduced pressure. The residue was treatedwith 200 mL water and the crude 2-methyl-propenoic acid2-[[(2-(4-hydroxy-3,5-di tert.butyl-phenyl)-methyl)amino]carbonyl]aminoethyl ester was isolated byfiltration. 2-methyl-propenoic acid 2-[[(2-(4-hydroxy-3,5-di tert.butyl-phenyl)-methyl)amino]carbonyl]aminoethyl ester was purified bypreparative column chromatography on a Merck SVP D40 column, using agradient elution from methylene chloride to methylene chloride/methanol90/10. 4.8 g (58%) 2-methyl-propenoic acid 2-[[(2-(4-hydroxy-3,5-ditert. butyl-phenyl)-methyl)amino]carbonyl]aminoethyl ester was isolated.Synthesis of Stabilizer-3:N-(4-hydroxy-3,5-dimethyl-benzyl)-methacrylamide

611 g (5 mol) 2,6-dimethyl-phenol was dissolved in 440 mL ethanol. 0.5 gphenothiazine was added as stabilizer. 718 g (5 mol)N-methoxymethyl-acrylamide was added over 15 minutes and the reactionmixture was heated to 55° C. 3 mL concentrated sulfuric acid was addeddrop wise, while the temperature was kept below 60° C. The reactionmixture was heated to 80° C. over 90 minutes and the reaction wasallowed to continue for 5 hours at 80° C. The reaction mixture wasallowed to cool down to 60° C. andN-(4-hydroxy-3,5-dimethyl-benzyl)-methacrylamide was forced tocrystallize by adding a small amount ofN-(4-hydroxy-3,5-dimethyl-benzyl)-methacrylamide. The reaction mixturewas further cooled to room temperature andN-(4-hydroxy-3,5-dimethyl-benzyl)-methacrylamide was isolated byfiltration. N-(4-hydroxy-3,5-dimethyl-benzyl)-methacrylamide was washedwith 180 mL ethanol and dried under reduced pressure at 50° C. 861 g(79%) of N-(4-hydroxy-3,5-dimethyl-benzyl)-methacrylamide was isolated(m.p.: 136-138° C.)

Example 9

This example illustrates the reduction in volatile extractables of thestabilizer from curable compositions including a polymerizablestabilizer compared to a non-polymerizable stabilizer.

Preparation of the Curable Compositions

The comparative liquid curable compositions COMP-22 to COMP-24 and theinventive liquid curable compositions INV-45 to INV-47 were prepared bymixing the components according to Table 20. The weight % (wt %) of thecomponents are based on the total weight of the curable composition.

TABLE 20 COMP- COMP- COMP- INV- INV- INV- wt % of 22 23 24 45 46 47 VEEA74.5 73.5 73.5 73.5 73.5 73.5 M600 20.0 20.0 20.0 20.0 20.0 20.0IRGACURE ™ 2.5 2.5 2.5 2.5 2.5 2.5 127 Tegosol 3.0 3.0 3.0 3.0 3.0 3.0BHT — 1.0 — — — — MPH — — 1.0 — — — STAB-1 — — — 1.0 — — STAB-2 — — — —1.0 — STAB-3 — — — — — 1.0

The comparison compositions COMP-23 and COMP-24 includenon-polymerizable stabilizers, while to the comparison compositionCOMP-22 no stabilizer was added.

Evaluation of the Curable Compositions

The comparative curable compositions COMP-22 to COMP-24 and theinventive curable compositions INV-45 to INV-47 were coated on PET100using a bar coater and a 10 μm wired bar. Each coated sample was curedusing a Fusion DRSE-120 conveyer, equipped with a Fusion VPS/1600 lamp(D-bulb), which transported the samples under the UV-lamp on a conveyerbelt at a speed of 20 m/min.

The curing was performed under a nitrogen inerting condition. The coatedsubstrate was mounted on the metal plate and on top a metal frame wasplaced of 1 cm height with a non-UV-absorbing quartz glass window, andthen filled during 30 seconds with pure nitrogen gas before the coatingwas placed on the conveyer belt.

All the samples were completely cured. The volatile extractables weremeasured according to the method of thermal desorption described above.The results are illustrated in Table 21.

TABLE 21 Estimated Peak of amount of Cured stabilizer extracted sampleof (fragments) stabilizer COMP-22 NO — COMP-23 YES 3.8 mg/m² COMP-24 YES4.3 mg/m² INV-45 NO — INV-46 NO — INV-47 NO —

The thermal desorption spectra of the comparison compositions COMP-2″and COMP-24 include a peak signal appointed to the non-polymerizablestabilizer. The thermal desorption spectra of the inventive samples didnot show a peak signal appointed to the polymerizable stabilizer.Therefore, the use of a polymerizable stabilizer is favourable forcurable compositions, especially in the case when the amount ofextractables needs to be minimized, for instance in the case of printingon food packages.

Example 10

This example illustrates the effect on the stability of a curablecomposition by the addition of a polymerizable stabilizer in a pigmentedink including a magenta pigment.

Preparation of the Magenta Dispersion CPD1

A concentrated pigment dispersion CPD1 was prepared by mixing for 30minutes the components according to Table 22 in a 1000 mL vessel using aDISPERLUX™ YELLOW075 (from DISPERLUX S.A.R.L., Luxembourg). The vesselwas then connected to a EIGER™ Lab Bead mill (from EIGER TORRANCE Ltd.)having a bead filling of 52% with 0.4 mm yttrium stabilized zirconiumoxide beads (“high wear resistant zirconia grinding media” from TOSOHCo.) and milling for 280 minutes. After milling the dispersion wasseparated from the beads using a filter cloth.

TABLE 22 Component Quantity RT355D 160.0 g S39000-sol 533.3 g Genorad 16 8.0 g VEEA  98.7 g

The average particle size of the concentrated pigmented dispersions CPD1was 95 nm measured with the Malvern Nano-S.

Preparation of the Curable Ink

The comparative pigmented curable inks COMP-25 to COMP-28 and theinventive pigmented curable inks INV-48 to INV-50 were prepared byadding to the magenta dispersion the components according to Table 23.The weight % (wt %) of the components are based on the total weight ofthe curable ink.

TABLE 23 wt % of COMP-25 COMP-26 COMP-27 COMP-28 INV-48 INV-49 INV-50CPD1 20.0 20.0 20.0 20.0 20.0 20.0 20.0 VEEA 54.5 53.5 53.5 53.5 53.553.5 53.5 M600 20.0 20.0 20.0 20.0 20.0 20.0 20.0 Irgacure ™ 2.5 2.5 2.52.5 2.5 2.5 2.5 127 Byksol 3.0 3.0 3.0 3.0 3.0 3.0 3.0 BHT — 1.0 — — — —— MPH — — 1.0 — — — Genorad ™ — — — 1.0 — — — 16 STAB-1 — — — 1.0 — —STAB-2 — — — — 1.0 — STAB-3 — — — — — 1.0

The comparison inks COMP-26 to COMP-28 include non-polymerizablestabilizers, while to the comparison ink COMP-25 no stabilizer wasadded.

Evaluation of the Curable Inks

The stability of the curable inks was evaluated according to the methoddescribed above.

The results are given in Table 24.

TABLE 24 Viscosity of Curable fresh Viscosity after ink formulation 6days at 83° C. COMP-25 15.3 solid COMP-26 18.0 solid COMP-27 14.6 solidCOMP-28 14.6 solid INV-48 15.4 19.8 INV-49 13.1 23.2 INV-50 9.6 11.8

From Table 24, it should be clear that the inventive inks INV-48 toINV-50 exhibit an improved stability compared to the comparison inksformulated from the same concentrated magenta pigment dispersion. Sincethe jetting process of inkjet inks, is very dependent upon the inkviscosity, the inventive polymerizable stabilizers deliver animprovement of viscosity stability in order to prevent that aged inkjetinks are not jettable anymore because unstable curable inkjet inksincrease in ink viscosity and even can solidify.

Example 11

This example illustrates the effect on the stability by the addition ofa polymerizable stabilizer in a pigmented ink including a yellowpigment.

Preparation of the Yellow Dispersion CPD2

A concentrated pigment dispersion CPD2 was prepared by mixing for 30minutes the components according to Table 25 in a 1000 mL vessel using aDISPERLUX™ YELLOW075 (from DISPERLUX S.A.R.L., Luxembourg). The vesselwas then connected to a EIGER™ Lab Bead mill (from EIGER TORRANCE Ltd.)having a bead filling of 52% with 0.4 mm yttrium stabilized zirconiumoxide beads (“high wear resistant zirconia grinding media” from TOSOHCo.) and milling for 200 minutes. After milling the dispersion wasseparated from the beads using a filter cloth.

TABLE 25 Component Quantity PY150 140.0 g S35000-SOL 466.7 g GENORAD ™16  7.0 g VEEA  86.3 g

The average particle size of the concentrated pigmented dispersions CPD2was 160 nm measured with the Malvern Nano-S.

Preparation of the Curable Inks

The comparative pigmented curable inks COMP-29 to COMP-31 and theinventive pigmented curable inks INV-51 and INV-52 were prepared byadding to the yellow dispersion CPD2 the components according to Table26. The weight % (wt %) of the components are based on the total weightof the curable composition.

TABLE 26 wt % of COMP-29 COMP-30 COMP-31 INV-51 INV-52 CPD2 15.0 15.015.0 15.0 15.0 VEEA 58.5 57.5 56.5 58.5 56.5 M600 20.0 20.0 20.0 20.020.0 IRGACURE ™ 2.5 2.5 2.5 2.5 2.5 127 Tegosol 3.0 3.0 3.0 3.0 3.0 BHT1.0 2.0 3.0 — — STAB-1 — — — 1.0 3.0Evaluation of the Curable Inks

The stability of the curable inks was evaluated according to the methoddescribed above.

The results are given in Table 27.

TABLE 27 Viscosity of Curable fresh Viscosity after ink formulation 6days at 83° C. COMP-29 30.6 solid COMP-30 30.6 solid COMP-31 30.6 solidINV-51 30.6 solid INV-52 30.6 28.7

The results of Table 27 illustrate that the use of the conventionalnon-polymerizable stabilizer BHT did not stabilize the ink, even in arelative high amount (3 wt %) (formulations COMP-29 to COMP-31). Theyellow pigmented ink was stabilized by the addition of 3 wt % of theinventive STAB-1 (ink INV-52). For some unknown reason, it was foundthat polymerizable inhibitors were more efficient. Since the jettingprocess of inkjet inks, is very dependent upon the ink viscosity, theinventive polymerizable stabilizers deliver an improvement of viscositystability in order to prevent that aged inkjet inks are not jettableanymore because unstable curable inkjet inks increase in ink viscosityand even can solidify.

Preparation of the Yellow Dispersion CPD3

A concentrated pigment dispersion CPD3 was prepared by mixing for 30minutes the components according to Table 28 in a 1000 mL vessel using aDISPERLUX™ YELLOW075 (from DISPERLUX S.A.R.L., Luxembourg). The vesselwas then connected to a EIGER™ Lab Bead mill (from EIGER TORRANCE Ltd.)having a bead filling of 52% with 0.4 mm yttrium stabilized zirconiumoxide beads (“high wear resistant zirconia grinding media” from TOSOHCo.) and milling for 220 minutes. After milling the dispersion wasseparated from the beads using a filter cloth.

TABLE 28 Component Quantity PY150-2 140.0 g S35000-SOL 466.7 g GENORAD ™16  7.0 g VEEA  86.3 g

The average particle size of the concentrated pigmented dispersions CPD3was 136 nm measured with the Malvern Nano-S.

Preparation of the Curable Inks

The comparative pigmented curable inks COMP-32 to COMP-34 and theinventive pigmented curable inks INV-53 and INV-54 were prepared byadding to the yellow dispersion CPD3 the components according to Table29. The weight % (wt %) of the components are based on the total weightof the curable composition.

TABLE 29 wt % of COMP-32 COMP-33 COMP-34 INV-53 INV-54 CPD3 15.0 15.015.0 15.0 15.0 VEEA 58.5 57.5 56.5 58.5 56.5 M600 20.0 20.0 20.0 20.020.0 IRGACURE ™ 2.5 2.5 2.5 2.5 2.5 127 Tegosol 3.0 3.0 3.0 3.0 3.0 BHT1.0 2.0 3.0 — — STAB-1 — — — 1.0 3.0Evaluation of the Curable Inks

The stability of the curable inks was evaluated according to the methoddescribed above.

The results are given in Table 30.

TABLE 30 Viscosity of Curable fresh Viscosity after ink formulation 6days at 83° C. COMP-32 28.4 solid COMP-33 28.4 solid COMP-34 28.4 solidINV-53 28.4 solid INV-54 28.4 23.1

Table 30 illustrated that the results are comparable for the first andsecond yellow pigment inks (compare with table 8). Also now, the yellowpigmented ink was not stabilized by 3 wt % BHT (formulation COMP-34),while it was already stable with 3 wt % STAB-1 (formulation INV-54).

Example 12

This example illustrates the effect on the stability by the addition ofa polymerizable stabilizer in a pigmented ink including a cyan pigment.

Preparation of the Cyan Dispersion CPD4

A concentrated pigment dispersion CPD4 was prepared by mixing for 30minutes the components according to Table 31 in a 1000 mL vessel using aDISPERLUX™ YELLOW075 (from DISPERLUX S.A.R.L., Luxembourg). The vesselwas then connected to a EIGER™ Lab Bead mill (from EIGER TORRANCE Ltd.)having a bead filling of 52% with 0.4 mm yttrium stabilized zirconiumoxide beads (“high wear resistant zirconia grinding media” from TOSOHCo.) and milling for 100 minutes. After milling the dispersion wasseparated from the beads using a filter cloth.

TABLE 31 Component Quantity PB15:4 140.0 g S35000-SOL 466.7 g GENORAD ™16  7.0 g VEEA  86.3 g

The average particle size of the concentrated pigmented dispersions CPD4was 139 nm measured with the Malvern Nano-S.

Preparation of the Curable Inks

The comparative pigmented curable inks COMP-35 and the inventivepigmented curable ink INV-55 were prepared by adding to the cyandispersion CPD4 the components according to Table 32. The weight % (wt%) of the components are based on the total weight of the curablecomposition.

TABLE 32 wt % of COMP-35 INV-55 CPD4 15.0 15.0 VEEA 52.0 51.0 M600 20.020.0 IRGACURE ™ 127 2.5 2.5 GENOPOL ™ TX-1 2.5 2.5 GENOPOL ™ AB-1 5.05.0 Tegosol 3.0 3.0 STAB-1 — 1.0Evaluation of the Curable Inks

The stability of the curable inks was evaluated according to the methoddescribed above.

The results are given in Table 33.

TABLE 33 Viscosity of Curable fresh Viscosity after ink formulation 6days at 83° C. COMP-35 18.1 solid INV-55 18.1 25.4

Table 33 illustrates that also a cyan ink can be stabilized with the useof the inventive polymerizable stabilizer STAB-1 (ink INV-55), while theink without stabilizer is not stable (formulation COMP-35). Since thejetting process of inkjet inks, is very dependent upon the inkviscosity, the inventive polymerizable stabilizers deliver animprovement of viscosity stability in order to prevent that aged inkjetinks are not jettable anymore because unstable curable inkjet inksincrease in ink viscosity and even can solidify.

Example 13

This example illustrates the effect of the amount of an inventivepolymerizable stabilizer to a pigmented ink including a magenta pigmenton the curing speed of the curable ink.

Preparation of the Curable Inks

The concentrated magenta pigment dispersion CPD1 of EXAMPLE 10 was usedto prepare the inks according to Table 34. The weight % (wt %) of thecomponents are based on the total weight of the curable composition.

TABLE 34 wt % of INV-56 INV-57 INV-58 INV-59 CPD1 20.0 20.0 20.0 20.0VEEA 51.5 48.5 42.5 30.5 M600 20.0 20.0 20.0 20.0 IRGACURE ™ 2.5 2.5 2.52.5 127 Tegosol 3.0 3.0 3.0 3.0 STAB-1 3.0 6.0 12.0 24.0Evaluation of the Curable Inks

The inventive curable inks INV-56 to INV-59 were coated on PET100 usinga bar coater and a 10 μm wired bar. Each coated sample was cured using aFusion DRSE-120 conveyer, equipped with a Fusion VPS/1600 lamp (D-bulb),which transported the samples under the UV-lamp on a conveyer belt at aspeed of 20 m/min. The curing was performed twice, a first time underambient air condition, the second time under nitrogen inertingcondition.

For curing under a nitrogen inerting condition, the coated substrate wasmounted on the metal plate and on top a metal frame was placed of 1 cmheight with a non-UV-absorbing quartz glass window, and then filledduring 30 seconds with pure nitrogen gas before the coating was placedon the conveyer belt.

The results are given in Table 35.

TABLE 35 Curing under Curing under Cured sample ambient air nitrogeninerting of condition condition INV-56 fully cured fully cured INV-57partially cured fully cured INV-58 partially cured fully cured INV-59partially cured fully cured

Table 35 illustrates the effect on the possibility to cure the pigmentedink, even in the case of a very high amount of stabilizer added to thepigmented ink. Under nitrogen inerting condition, the curing iscomplete, even in the case of 24 wt % STAB-1 (ink INV-59). Thus, theability to stabilize the pigmented ink against unwanted polymerizationduring the storage of the ink by the addition of the polymerizablestabilizer appears not to be accompanied by a loss in curing speed undernitrogen inerting condition.

Example 14

This example illustrates the effect of a polymerizable compound A havingan acrylate group and a methacrylate group on the level of extractables.

Preparation of the Free Radical Curable Liquids

The free radical curable liquids COMP-36 and COMP-37 were prepared inthe same manner as in EXAMPLE 3, but using the compounds according toTable 36.

TABLE 36 wt % of COMP-36 COMP-37 CM-1 94.50 74.50 M600 — 20.00Irgacure ™ 2.50 2.50 127 BYKSOL 3.00 3.00

The synthesis of the polymerizable compound CM-1 is given above inEXAMPLE 1.

Preparation and Evaluation of Cured Samples

The coated samples of the free radical curable liquids COMP-36 andCOMP-37 were prepared and cured in the exactly the same manner asdisclosed by EXAMPLE 2.

The curing degree was determined for the cured samples of the freeradical curable liquids COMP-36 and COMP-37. Both cured samples of thefree radical curable liquids COMP-36 and COMP-37 appeared to be fullycured. However, the cured sample of COMP-36 exhibited a strong smell.The amount of volatile extractables by thermal desorption was determinedfor both cured samples. The results are shown in Table 37.

TABLE 37 Cured sample Curing TDE- of degree level COMP-36 fully badcured COMP-37 fully poor cured

The results in Table 37 show that a monomer having an acrylate group anda methacrylate group cannot replace the polymerizable compound A.

Example 15

This example illustrates that free radical curable inks in accordancewith the present invention, but lacking an initiator can be fully curedby using electron beam curing to exhibit low amounts of extractables.

Preparation of the Cyan Dispersion CPD5

4.0 kg of the polymeric dispersant DB162 and 267 g of the polymerizationinhibitor GENORAD™ 16 were dissolved in 18.4 kg of DPGDA in a vessel of50 L. 8.0 kg of cyan pigment PB15:4 was added to the solution andstirred for 10 minutes using a DISPERLUX™ disperser (from DISPERLUXS.A.R.L., Luxembourg). The vessel was then connected to a NETZSCH™ LMZ10mill (from NETZSCH-Feinmahltechnik GmbH, Germany) having an internalvolume of 10 L filled for 52% with 0.4 mm yttrium stabilized zirconiabeads (“high wear resistant zirconia grinding media” from TOSOH Co.).The mixture was circulated over the mill for 245 minutes at a rotationspeed in the mill of about 15 m/s. During the complete milling procedurethe content of the mill was cooled to a temperature of 42° C. Theconcentrated pigment dispersion CPD5 was discharged into another 60 Lvessel. After circulating it over the mill, 13.3 kg of a 30 wt %solution of DB162 in DPGDA was added to the dispersion. The resultingconcentrated pigment dispersion CPD5 according to Table 38 exhibited anaverage particle size of 110 nm.

TABLE 38 wt % of dispersion CPD5 PB15:4 15 Disperbyk162- 15 sol Genorad16 1 DPGDA 69Preparation of the Cyan Dispersion CPD6

A concentrated pigment dispersion CPD6 was prepared by mixing for 30minutes the componentw according to Table 39 in a 1000 mL vessel using aDISPERLUX™ YELLOW075 (from DISPERLUX S.A.R.L., Luxembourg). The vesselwas then connected to a EIGER™ Lab Bead mill (from EIGER TORRANCE Ltd.)having abead filling of 52% with 0.4 mm yttrium stabilized zirconiumbeads (“high wear resistant zirconia grinding media” from TOSOH Co.) andmilling for 100 minutes. After milling the dispersion was separated fromthe beads using a filter cloth.

TABLE 39 Component dispersion CPD6 PB15:4 140.0 g S35000-sol 466.7 gGenorad 16  7.0 g VEEA  86.3 gPreparation of the Curable Inks

The comparative pigmented curable ink COMP-38 and the inventivepigmented curable ink INV-60 were prepared by adding to the concentratedcyan dispersion CPD5 respectively CPD6 the components according to Table40. The weight % (wt %) of the components are based on the total weightof the curable ink

TABLE 40 wt % of component: COMP-38 INV-60 dispersion 15.20 — CPD5dispersion — 13.04 CPD6 DPGDA 84.80 — VEEA — 69.57 M600 — 17.39Evaluation of the Curable Inks

The comparative pigmented curable ink COMP-38 and the inventivepigmented curable ink INV-60 were coated on PET100 using a bar coaterand a 10 μm wired bar.

The coating was first brought into a nitrogen inerting condition by aflow of nitrogen gas of 4.5 bar which was led to the sample chamber ofthe EB-equipment to replace air by nitrogen, and then the coating wastransported to be cured by the EB.

The coating was cured with e-beam using Dürr EB-equipment at anaccelerating voltage of 180 kV and a current of 7 mA at a transportspeed of 14 m/min, resulting in a dose of 60 kGy.

The amount of volatile extractables by thermal desorption was determinedand is shown in Table 41.

TABLE 41 Cured sample Curing TDE- of degree level COMP-38 fully curedbad INV-60 fully cured acceptable

From Table 41, it is clear that small amount of volatile extractables bythermal desorption were observed for a free radical curable inkjet inkin accordance with the present invention lacking a initiator and curedby electron beam.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

The invention claimed is:
 1. A free radical curable liquid for use inprinting, the free radical curable liquid comprising: one or morephotoinitiators selected from a polymerizable initiator having athioxanthone group and the group consisting of non-polymeric di- ormultifunctional initiators, oligomeric initiators, polymeric initiators,and polymerizable initiators; wherein all polymerizable compounds,including any polymerizable initiator, in the free radical curableliquid form a polymerizable composition consisting essentially of:25-100 wt % of one or more polymerizable compounds (A) having at leastone acrylate group (G1) and at least one ethylenically unsaturatedpolymerizable functional group (G2) selected from the group consistingof a vinylether group, an allylether group, and an allylester group;0-55 wt % of one or more polymerizable compounds (B) selected from thegroup consisting of monofunctional acrylates and difunctional acrylates;and 0-55 wt % of one or more polymerizable compounds (C) selected fromthe group consisting of trifunctional acrylates, tetrafunctionalacrylates, pentafunctional acrylates, and hexafunctional acrylates,wherein if the weight percentage of compounds (B) >24 wt %, then theweight percentage of compounds (C) >1 wt %; wherein all weightpercentages of (A), (B), and (C) are based upon a total weight of thepolymerizable composition; and the one or more photoinitiators selectedfrom the group consisting of non-polymeric di- or multifunctionalinitiators, oligomeric initiators, polymeric initiators, andpolymerizable initiators contain a photoinitiating group selected fromthe group consisting of a benzophenone group, a 1,2-diketone group, andan anthraquinone group.
 2. The free radical curable liquid according toclaim 1, wherein the compound (A) is represented by the Formula (I):

wherein (GX) and (GY) are independently selected from the groupconsisting of (G1) and (G2); n and m are independently selected integershaving a value of 0 or 1; and L represents a (n+m+2)-valent linkinggroup including at least one carbon atom.
 3. The free radical curableliquid according to claim 2, wherein the integers n and m both have avalue equal to
 0. 4. The free radical curable liquid according to claim1, wherein a molecular weight of compound (A) is smaller than 800Dalton.
 5. The free radical curable liquid according to claim 1, whereinthe ethylenically unsaturated polymerizable functional group (G2) is avinylether group.
 6. The free radical curable liquid according to claim1, wherein the polymerizable composition includes 60 wt % to 90 wt % ofone or more polymerizable compounds (A) and 10 wt % to 40 wt % of one ormore polymerizable compounds (C).
 7. The free radical curable liquidaccording to claim 1, wherein the liquid includes a polymerizablephotoinitiator.
 8. A free radical curable printing ink comprising: acolorant; and the free radical curable liquid according to claim
 1. 9.The free radical curable printing ink according to claim 8, wherein thecolorant is a pigment.
 10. A packaging material for packaging foodcomprising: a cured layer of the free radical curable printing inkaccording to claim
 8. 11. A printing method comprising: providing thefree radical curable liquid as defined by claim 1; and applying a layerof the free radical curable liquid on a substrate.
 12. The printingmethod according to claim 11, wherein the layer includes a pigment. 13.The printing method according to claim 11, wherein the layer is a whitelayer including a titanium dioxide pigment.
 14. The printing methodaccording to claim 11, wherein the layer is applied by: a printingtechnique selected from the group consisting of inkjet printing,flexographic printing, offset printing, and screen printing; or acoating technique selected from the group consisting of dip coating,knife coating, extrusion coating, spin coating, slide hopper coating,and curtain coating.
 15. The printing method according to claim 11,further comprising the step of curing the layer with electron beams. 16.The free radical curable liquid according to claim 1, wherein the freeradical curable liquid is a free radical curable inkjet liquid.
 17. Thefree radical curable liquid according to claim 1, wherein the freeradical curable liquid is a UV radiation free radical curable inkjetliquid.
 18. The free radical curable printing ink according to claim 8,wherein the free radical curable printing ink is a free radical curableinkjet ink.
 19. A UV-curable pigment inkjet ink set including a freeradical curable inkjet ink according to claim
 18. 20. A free radicalcurable liquid for use in printing, the free radical curable liquidcomprising: one or more photoinitiators selected from the groupconsisting of non-polymeric di- or multifunctional initiators,oligomeric initiators, polymeric initiators, and polymerizableinitiators; wherein all polymerizable compounds, including anypolymerizable initiator, in the free radical curable liquid form apolymerizable composition consisting of: 25-100 wt % of one or morepolymerizable compounds (A) having at least one acrylate group (G1) andat least one ethylenically unsaturated polymerizable functional group(G2) selected from the group consisting of a vinylether group, anallylether group, and an allylester group; 0-55 wt % of one or morepolymerizable compounds (B) selected from the group consisting ofdifunctional acrylates; and 0-55 wt % of one or more polymerizablecompounds (C) selected from the group consisting of trifunctionalacrylates, tetrafunctional acrylates, pentafunctional acrylates, andhexafunctional acrylates, wherein if the weight percentage of compounds(B) >24 wt %, then the weight percentage of compounds (C) >1 wt %;wherein all weight percentages of (A), (B), and (C) are based upon atotal weight of the polymerizable composition.
 21. A free radicalcurable printing ink comprising: a colorant; and the free radicalcurable liquid according to claim
 20. 22. The free radical curableprinting ink according to claim 21, wherein the colorant is a pigment.23. The free radical curable printing ink according to claim 21, whereinthe free radical curable printing ink is a free radical curable inkjetink.